go/build: do not suggest runtime.Version in comment

The form of runtime.Version is not guaranteed to be helpful.
Do not suggest it. (The suggestion was added in CL 136215.)

Change-Id: I3227d2e66b6ce860b7e62d7ba531c18fb173823c
Reviewed-on: https://go-review.googlesource.com/c/149258
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/go/build/doc.go

@@ -111,8 +111,7 @@
 //	- "go1.12", from Go version 1.12 onward
 //	- any additional words listed in ctxt.BuildTags
 //
-// There are no build tags for beta or minor releases. Programs that need the
-// minor release number can call runtime.Version.
+// There are no build tags for beta or minor releases.
 //
 // If a file's name, after stripping the extension and a possible _test suffix,
 // matches any of the following patterns: