[clang-format][NFC] Removed unused include

clang/unittests/Format/FormatTestComments.cpp

 //===- unittest/Format/FormatTestComments.cpp - Formatting unit tests -----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Format/Format.h"
 
 #include "../Tooling/ReplacementTest.h"
 #include "FormatTestUtils.h"
 
 #include "llvm/Support/Debug.h"
-#include "llvm/Support/MemoryBuffer.h"
 #include "gtest/gtest.h"
 
 #define DEBUG_TYPE "format-test"
 
 using clang::tooling::ReplacementTest;
 
 namespace clang {
 namespace format {