Ninja: Fix regression in .rsp file support

In commit a390de65 (Ninja: Generate separate compile and link rules for
each target, 2015-05-18) we removed the _RSP_FILE suffix from rule names
meant for targets that need to build with a .rsp file because we now use
per-target rules anyway.  Remove this suffix from references to the rule
too.

Reported-by: Herz Thomas <Thomas.Herz@kuka.com>

Source/cmGlobalNinjaGenerator.cxx

@@ -233,7 +233,6 @@ void cmGlobalNinjaGenerator::WriteBuild(std::ostream& os,
   if (cmdLineLimit > 0
       && args.size() + buildstr.size() + assignments.size()
                                                     > (size_t) cmdLineLimit) {
-    buildstr += "_RSP_FILE";
     variable_assignments.str(std::string());
     cmGlobalNinjaGenerator::WriteVariable(variable_assignments,
                                           "RSP_FILE", rspfile, "", 1);