runtime: remove nextSampleNoFP from plan9

Plan 9 can use floating point now.

Change-Id: If721b243daa31853609cb3d2c535d86c106a1ee1
Reviewed-on: https://go-review.googlesource.com/c/go/+/655879
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>

src/runtime/malloc.go

@@ -1815,13 +1815,6 @@ func nextSample() int64 {
 		// Sample immediately.
 		return 0
 	}
-	if GOOS == "plan9" {
-		// Plan 9 doesn't support floating point in note handler.
-		if gp := getg(); gp == gp.m.gsignal {
-			return nextSampleNoFP()
-		}
-	}
-
 	return int64(fastexprand(MemProfileRate))
 }
 
@@ -1855,20 +1848,6 @@ func fastexprand(mean int) int32 {
 	return int32(qlog*(minusLog2*float64(mean))) + 1
 }
 
-// nextSampleNoFP is similar to nextSample, but uses older,
-// simpler code to avoid floating point.
-func nextSampleNoFP() int64 {
-	// Set first allocation sample size.
-	rate := MemProfileRate
-	if rate > 0x3fffffff { // make 2*rate not overflow
-		rate = 0x3fffffff
-	}
-	if rate != 0 {
-		return int64(cheaprandn(uint32(2 * rate)))
-	}
-	return 0
-}
-
 type persistentAlloc struct {
 	base *notInHeap
 	off  uintptr