all: clean up old go build constraints

The go directive in all 3 go.mod files is 1.23.0, so build constraints
go1.20, go1.21, and go1.22 are always satisfied. No need to check them.

Change-Id: I8c34a0fcc3486f6561aa4013d4bb9ce284f4d57d
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/673275
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Peter Weinberger <pjw@google.com>
diff --git a/counter/countertest/countertest.go b/counter/countertest/countertest.go
index 533f5e5..3f0ad9e 100644
--- a/counter/countertest/countertest.go
+++ b/counter/countertest/countertest.go
@@ -8,6 +8,7 @@
 
 import (
 	"sync"
+	"testing"
 
 	"golang.org/x/telemetry/counter"
 	ic "golang.org/x/telemetry/internal/counter"
@@ -61,3 +62,10 @@
 func ReadFile(name string) (counters, stackCounters map[string]uint64, _ error) {
 	return ic.ReadFile(name)
 }
+
+func init() {
+	// Extra safety check.
+	if !testing.Testing() {
+		panic("use of this package is disallowed in non-testing code")
+	}
+}
diff --git a/counter/countertest/countertest_go121.go b/counter/countertest/countertest_go121.go
deleted file mode 100644
index 8d117e0..0000000
--- a/counter/countertest/countertest_go121.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright 2023 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build go1.21
-
-package countertest
-
-import "testing"
-
-func init() {
-	// Extra safety check for go1.21+.
-	if !testing.Testing() {
-		panic("use of this package is disallowed in non-testing code")
-	}
-}
diff --git a/counter/countertest/countertest_test.go b/counter/countertest/countertest_test.go
index 2379445..5993230 100644
--- a/counter/countertest/countertest_test.go
+++ b/counter/countertest/countertest_test.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.21
-
 package countertest
 
 import (
diff --git a/internal/configgen/main.go b/internal/configgen/main.go
index 145ffd9..afc9258 100644
--- a/internal/configgen/main.go
+++ b/internal/configgen/main.go
@@ -4,8 +4,6 @@
 
 //go:generate go run . -w
 
-//go:build go1.22
-
 // Package configgen generates the upload config file stored in the config.json
 // file of golang.org/x/telemetry/config based on the chartconfig stored in
 // config.txt.
diff --git a/internal/configgen/main_test.go b/internal/configgen/main_test.go
index 2651d7a..0d1f82e 100644
--- a/internal/configgen/main_test.go
+++ b/internal/configgen/main_test.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.22
-
 package main
 
 import (
diff --git a/internal/configgen/syslist.go b/internal/configgen/syslist.go
index 6b5012f..d621d74 100644
--- a/internal/configgen/syslist.go
+++ b/internal/configgen/syslist.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.22
-
 package main
 
 // knownOS is the list of past, present, and future known GOOS values.
diff --git a/internal/configgen/validate.go b/internal/configgen/validate.go
index 1652767..6f38362 100644
--- a/internal/configgen/validate.go
+++ b/internal/configgen/validate.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.22
-
 package main
 
 import (
diff --git a/internal/configgen/validate_test.go b/internal/configgen/validate_test.go
index ec6f383..6519eb5 100644
--- a/internal/configgen/validate_test.go
+++ b/internal/configgen/validate_test.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.22
-
 package main
 
 import (
diff --git a/internal/mmap/mmap_other.go b/internal/mmap/mmap_other.go
index 190afd8..610ab1a 100644
--- a/internal/mmap/mmap_other.go
+++ b/internal/mmap/mmap_other.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (js && wasm) || wasip1 || plan9 || (solaris && !go1.20)
+//go:build (js && wasm) || wasip1 || plan9
 
 package mmap
 
diff --git a/internal/mmap/mmap_unix.go b/internal/mmap/mmap_unix.go
index f15ac61..72ad91d 100644
--- a/internal/mmap/mmap_unix.go
+++ b/internal/mmap/mmap_unix.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build unix && (!solaris || go1.20)
+//go:build unix
 
 package mmap