cmd/compile: remove no-longer-necessary call to calculateDepths

We now calculate depths by default, no need to ask.
All calls were removed in CL 680775 when that CL was written, but an
additional call appeared between then and submitting the CL. Oops.

Another case for which a presubmit check would help.

Fixes #74762

Change-Id: I1b70ed7f91b56e4939b4a3d0ad7a5f31fe396b4c
Reviewed-on: https://go-review.googlesource.com/c/go/+/690036
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: t hepudds <thepudds1460@gmail.com>

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

@@ -15,7 +15,7 @@ type loop struct {
 	// Next three fields used by regalloc and/or
 	// aid in computation of inner-ness and list of blocks.
 	nBlocks int32 // Number of blocks in this loop but not within inner loops
-	depth   int16 // Nesting depth of the loop; 1 is outermost. Initialized by calculateDepths().
+	depth   int16 // Nesting depth of the loop; 1 is outermost.
 	isInner bool  // True if never discovered to contain a loop
 
 	// True if all paths through the loop have a call.

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

@@ -82,7 +82,6 @@ func loopRotate(f *Func) {
 
 	// Order loops to rotate any child loop before adding its top block
 	// to the parent loop's 'after' list.
-	loopnest.calculateDepths()
 	loopOrder := f.Cache.allocIntSlice(len(loopnest.loops))
 	for i := range loopOrder {
 		loopOrder[i] = i