gopls: tidy module

Change-Id: Id46de70e0ca1670cb2ba0cd0961b49896e5384fd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/313929
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/go.mod

@@ -9,7 +9,6 @@ require (
 	golang.org/x/mod v0.4.2
 	golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57
 	golang.org/x/tools v0.1.0
-	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
 	honnef.co/go/tools v0.1.3
 	mvdan.cc/gofumpt v0.1.1
 	mvdan.cc/xurls/v2 v2.2.0