Revert "[release-branch.go1.12] cmd/go: fix the default build output name for versioned binaries"

This reverts commit 746edd45 (CL 167384).

Reason for revert: Dmitri identified a potential problem in https://go-review.googlesource.com/c/go/+/140863/11#message-db0ff6bb2c7b06161ca47de771c4465afa8b1102, and we'd like more time to investigate without holding up the 1.12 release branch.

Updates #27283
Updates #30266
Updates #30821

Change-Id: I49d7bbbe200e80b81899c3bcbf7844717af010aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/167617


Reviewed-by: Andrew Bonventre <andybons@golang.org>