[llvm-mt] Remove platform-specific path in test

Summary:
Remove a platform-specific path separator added to the llvm-mt help text test
in https://reviews.llvm.org/D41732.

Test Plan: `check-llvm`



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321881 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed