go/gcimporter15: revert user-visible changes related to aliases

Reason: Decision to back out current alias implementation.
For golang/go#16339 (comment).

Change-Id: Id2a394d78a8661c767bcc05370b81f79d9bfb714
Reviewed-on: https://go-review.googlesource.com/32756
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Manghane <cmang@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
8 files changed