test,internal/testdir: don't set GOOS/GOARCH
The test directory driver currently sets the GOOS/GOARCH environment
variables if they aren't set. This appears to be in service of a
single test, test/env.go, which was introduced in September 2008 along
with os.Getenv. It's not entirely clear what that test is even trying
to check, since runtime.GOOS isn't necessarily the same as $GOOS. We
keep the test around because golang.org/x/tools/go/ssa/interp uses it
as a test case, but we simplify the test and eliminate the need for
the driver to set GOOS/GOARCH.
Change-Id: I5acc0093b557c95d1f0a526d031210256a68222d
Reviewed-on: https://go-review.googlesource.com/c/go/+/493601
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>