strings: remove a redundant and flaky part of a test

Fixes #35280

Change-Id: I6fa3747ff7b92c6fcabdf8692d85e103de55859f
Reviewed-on: https://go-review.googlesource.com/c/go/+/204598
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/strings/builder_test.go

@@ -178,21 +178,6 @@ func TestBuilderWriteByte(t *testing.T) {
 }
 
 func TestBuilderAllocs(t *testing.T) {
-	var b Builder
-	const msg = "hello"
-	b.Grow(len(msg) * 2) // because AllocsPerRun does an extra "warm-up" iteration
-	var s string
-	allocs := int(testing.AllocsPerRun(1, func() {
-		b.WriteString("hello")
-		s = b.String()
-	}))
-	if want := msg + msg; s != want {
-		t.Errorf("String: got %#q; want %#q", s, want)
-	}
-	if allocs > 0 {
-		t.Fatalf("got %d alloc(s); want 0", allocs)
-	}
-
 	// Issue 23382; verify that copyCheck doesn't force the
 	// Builder to escape and be heap allocated.
 	n := testing.AllocsPerRun(10000, func() {