remove FIXME comment (fixed with r284424); NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284427 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/sar_fold64.ll

@@ -71,8 +71,6 @@ define i8 @all_sign_bit_ashr(i8 %x) {
   ret i8 %sar
 }
 
-; FIXME
-
 define <4 x i32> @all_sign_bit_ashr_vec(<4 x i32> %x) {
 ; CHECK-LABEL: all_sign_bit_ashr_vec:
 ; CHECK:       # BB#0: