Revert "[Clang] Make rewrite-includes-bom.c work with internal shell"

This reverts commit 8d6470f.

This was causing a failure on the llvm-clang-aarch64-darwin builder when
using the external shell.

Author: boomanaiden154

clang/test/Frontend/rewrite-includes-bom.c

@@ -1,7 +1,8 @@
-// RUN: cat %S/Inputs/rewrite-includes-bom.h | od -t x1 | grep -q 'ef bb bf'
+// RUN: grep -q $'^\xEF\xBB\xBF' %S/Inputs/rewrite-includes-bom.h
 // RUN: %clang_cc1 -E -frewrite-includes -I %S/Inputs %s -o %t.c
-// RUN: cat %t.c | od -t x1 | not grep -q 'ef bb bf'
+// RUN: ! grep -q $'\xEF\xBB\xBF' %t.c
 // RUN: %clang_cc1 -fsyntax-only -verify %t.c
 // expected-no-diagnostics
+// REQUIRES: shell
 
 #include "rewrite-includes-bom.h"