cmd/compile: remove 68857 ModU flowLimit workaround in prove
We can know this is correct because all the testcases added by CL 605156 are still passing.
Partial revert of CL 605156 (everything but the testcases).
Change-Id: I5d8daadb4cb35a9de29daaabc22baee642511fe0
Reviewed-on: https://go-review.googlesource.com/c/go/+/714941 Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com> Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>