cmd/go: remove test checking GO386=387 invalidates cache
Since GO386=387 is no longer supported, this change deletes a cmd/go
test checking that building something with GO386=387, and then with
sse2, invalidated the build cache.
Fixes the longtest builders.
Change-Id: I5f645ef4ddf1cddb26dcf9390cee94907fc45a70
Reviewed-on: https://go-review.googlesource.com/c/go/+/259017
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>