cmd/compile: remove 68857 min & max flowLimit workaround in prove
We can know this is correct because all the testcases added by CL 656157 are still passing.
Partial revert of CL 656157 (everything but the testcases).
Change-Id: I24931fa1affba7e9e92233b3de74ebade3d48a09
Reviewed-on: https://go-review.googlesource.com/c/go/+/714921
Auto-Submit: Jorropo <jorropo.pgm@gmail.com> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>