cmGeneratedFileStream: clang-tidy applied to remove redundant `c_str` calls

After changing the ``cmGeneratedFileStream`` methods to accept
``std::string const&`` instead of ``const char*`` we don't
need to call ``std::string::c_str`` anymore when passing
a ``std::string`` to a ``cmGeneratedFileStream`` method.

This patch removes all redundant ``std::string::c_str``
calls when passing a string to a ``cmGeneratedFileStream`` method.

It was generated by building CMake with clang-tidy enabled using
the following options:

-DCMAKE_CXX_CLANG_TIDY=/usr/bin/clang-tidy-4.0;-checks=-*,readability-redundant-string-cstr;-fix;-fix-errors

Source/cmExtraSublimeTextGenerator.cxx

@@ -91,7 +91,7 @@ void cmExtraSublimeTextGenerator::CreateNewProjectFile(
 {
   const cmMakefile* mf = lgs[0]->GetMakefile();
 
-  cmGeneratedFileStream fout(filename.c_str());
+  cmGeneratedFileStream fout(filename);
   if (!fout) {
     return;
   }