[dev.regabi] runtime: delete gosave function

[dev.regabi] runtime: delete gosave function

The runtime.gosave function is not used anywhere. Delete.

Note: there is also a gosave<> function, which is actually used
and not deleted.

Change-Id: I64149a7afdd217de26d1e6396233f2becfad7153
Reviewed-on: https://go-review.googlesource.com/c/go/+/289719
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>