cmd/compile: remove bug workarounds in prove's loop inversion

I wrote theses checks because I got bad panics on some innocent functions,
turns out I was working around #63955 but I was not aware of that at the time.

The proper fix was included in CL 539977 this is now doing nothing.

Change-Id: I89329329933527b6f3cb817dc1e039a38f58da9a
Reviewed-on: https://go-review.googlesource.com/c/go/+/560975
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/ssa/prove.go

@@ -878,34 +878,17 @@ func prove(f *Func) {
 			continue
 		}
 
-		header := ind.Block
-		check := header.Controls[0]
-		if check == nil {
-			// we don't know how to rewrite a loop that not simple comparison
-			continue
-		}
-		switch check.Op {
-		case OpLeq64, OpLeq32, OpLeq16, OpLeq8,
-			OpLess64, OpLess32, OpLess16, OpLess8:
-		default:
-			// we don't know how to rewrite a loop that not simple comparison
-			continue
-		}
-		if !((check.Args[0] == ind && check.Args[1] == end) ||
-			(check.Args[1] == ind && check.Args[0] == end)) {
-			// we don't know how to rewrite a loop that not simple comparison
-			continue
-		}
 		if end.Block == ind.Block {
 			// we can't rewrite loops where the condition depends on the loop body
 			// this simple check is forced to work because if this is true a Phi in ind.Block must exists
 			continue
 		}
 
+		check := ind.Block.Controls[0]
 		// invert the check
 		check.Args[0], check.Args[1] = check.Args[1], check.Args[0]
 
-		// invert start and end in the loop
+		// swap start and end in the loop
 		for i, v := range check.Args {
 			if v != end {
 				continue