cmd/go: replace some calls to base.AppendPWD with cmd.Environ
With #50599 implemented, base.AppendPWD is redundant if cmd.Env would
otherwise be nil, and calls to os.Environ followed by base.AppendPWD
can be replaced by a simpler call to cmd.Environ.
Updates #50599.
Change-Id: I94a22e2a4cc8e83c815ac41702ea0b1ee5034ecc
Reviewed-on: https://go-review.googlesource.com/c/go/+/401534
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>