term: unify ioctl{Read,Write}Termios definition for aix, linux, solaris & zos

These all use TCGETS/TCSETS. Rather than having a term_unix_$GOOS.go
file for each platform, unify them in a single file.

Change-Id: Iefeeadf9cf53d8fa32b1b15b8169744a819565c8
Reviewed-on: https://go-review.googlesource.com/c/term/+/314231
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/term_unix_aix.go b/term_unix_aix.go
deleted file mode 100644
index e722809..0000000
--- a/term_unix_aix.go
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2019 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 aix
-// +build aix
-
-package term
-
-import "golang.org/x/sys/unix"
-
-const ioctlReadTermios = unix.TCGETS
-const ioctlWriteTermios = unix.TCSETS
diff --git a/term_unix_linux.go b/term_unix_linux.go
deleted file mode 100644
index 2d5efd2..0000000
--- a/term_unix_linux.go
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2019 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.
-
-package term
-
-import "golang.org/x/sys/unix"
-
-const ioctlReadTermios = unix.TCGETS
-const ioctlWriteTermios = unix.TCSETS
diff --git a/term_unix_zos.go b/term_unix_other.go
similarity index 63%
rename from term_unix_zos.go
rename to term_unix_other.go
index 9ef1246..1e8955c 100644
--- a/term_unix_zos.go
+++ b/term_unix_other.go
@@ -1,9 +1,9 @@
-// Copyright 2020 The Go Authors. All rights reserved.
+// Copyright 2021 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 zos
-// +build zos
+//go:build aix || linux || solaris || zos
+// +build aix linux solaris zos
 
 package term
 
diff --git a/term_unix_solaris.go b/term_unix_solaris.go
deleted file mode 100644
index 2d5efd2..0000000
--- a/term_unix_solaris.go
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2019 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.
-
-package term
-
-import "golang.org/x/sys/unix"
-
-const ioctlReadTermios = unix.TCGETS
-const ioctlWriteTermios = unix.TCSETS