Fix for r42230, MSVC test failure in DependencyDirectivesSourceMinimizerTest.cpp

r362459 introduced DependencyDirectivesSourceMinimizerTest.cpp, which
hits an MSVC bug:
developercommunity.visualstudio.com/content/problem/67300/stringifying-raw-string-literal.html

This only happens when the parameter to a macro is stringified in the
macro.  This patch removes the string from the assert so that the
warning no longer happens.

llvm-svn: 363074