runtime: rewrite map size test

I don't know why the memstats code is flaky.

TBR=bradfitz
CC=golang-dev
https://golang.org/cl/12160043

src/pkg/runtime/hashmap.c

@@ -1113,6 +1113,9 @@ runtime·makemap_c(MapType *typ, int64 hint)
 
 	key = typ->key;
 	
+	if(sizeof(Hmap) > 48)
+		runtime·panicstring("hmap too large");
+
 	if(hint < 0 || (int32)hint != hint)
 		runtime·panicstring("makemap: size out of range");
 

src/pkg/runtime/map_test.go

@@ -371,44 +371,3 @@ func testMapLookups(t *testing.T, m map[string]string) {
 		}
 	}
 }
-
-func TestMapSize(t *testing.T) {
-	if runtime.GOMAXPROCS(-1) != 1 {
-		t.Skip("gomaxprocs > 1 - not accurate")
-	}
-	var m map[struct{}]struct{}
-	size := bytesPerRun(100, func() {
-		m = make(map[struct{}]struct{})
-	})
-	if size > 48 {
-		t.Errorf("size = %v; want <= 48", size)
-	}
-}
-
-// like testing.AllocsPerRun, but for bytes of memory, not number of allocations.
-func bytesPerRun(runs int, f func()) (avg float64) {
-	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
-
-	// Warm up the function
-	f()
-
-	// Measure the starting statistics
-	var memstats runtime.MemStats
-	runtime.ReadMemStats(&memstats)
-	sum := 0 - memstats.Alloc
-
-	// Run the function the specified number of times
-	for i := 0; i < runs; i++ {
-		f()
-	}
-
-	// Read the final statistics
-	runtime.ReadMemStats(&memstats)
-	sum += memstats.Alloc
-
-	// Average the mallocs over the runs (not counting the warm-up).
-	// We are forced to return a float64 because the API is silly, but do
-	// the division as integers so we can ask if AllocsPerRun()==1
-	// instead of AllocsPerRun()<2.
-	return float64(sum / uint64(runs))
-}