Partial revert of "[llvm-ar] Document response file support in --help"

This is partial revert of 70a8027c60.

The test apparently failed on win32 bots due to the way slashes in
pathnames are handled.

llvm-svn: 364705

llvm/test/tools/llvm-ar/response-file.test

@@ -1,9 +0,0 @@
-RUN: touch %t-a.txt %t-b.txt %t-c.txt
-RUN: echo "rcs %t.a %t-a.txt %t-b.txt %t-c.txt" > %t-response
-RUN: rm -f %t.a
-RUN: llvm-ar @%t-response
-RUN: llvm-ar t %t.a | FileCheck %s
-
-CHECK:      a.txt
-CHECK-NEXT: b.txt
-CHECK-NEXT: c.txt