all: remove golang.org/x/xerrors dependency

The required functionality from golang.org/x/xerrors has been added to
the standard errors package.

Change-Id: Icec416521bf4511159e2577a778c941caf73a2bb
GitHub-Last-Rev: b28672c0972a5e92369076baff0c97c98c031ab3
GitHub-Pull-Request: golang/mod#8
Reviewed-on: https://go-review.googlesource.com/c/mod/+/400314
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Aofei Sheng <aofei@aofeisheng.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
diff --git a/go.mod b/go.mod
index 556fa50..e33eddd 100644
--- a/go.mod
+++ b/go.mod
@@ -5,5 +5,4 @@
 require (
 	golang.org/x/crypto v0.0.0-20210921155107-089bfa567519
 	golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e
-	golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898
 )
diff --git a/go.sum b/go.sum
index 9377c84..659a441 100644
--- a/go.sum
+++ b/go.sum
@@ -14,5 +14,3 @@
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e h1:aZzprAO9/8oim3qStq3wc1Xuxx4QmAGriC4VU4ojemQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
-golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/module/module.go b/module/module.go
index 795d076..c26d1d2 100644
--- a/module/module.go
+++ b/module/module.go
@@ -102,9 +102,9 @@
 	"strings"
 	"unicode"
 	"unicode/utf8"
+	"errors"
 
 	"golang.org/x/mod/semver"
-	errors "golang.org/x/xerrors"
 )
 
 // A Version (for clients, a module.Version) is defined by a module path and version pair.