VS,Xcode: Remove unused CMAKE_GENERATOR_* variables

Since the topic merged to master by commit 34a02846 (Merge topic
'ide-compiler-id', 2012-08-24), these variables are not used by
CMakeDetermine*Compiler.cmake for VS and Xcode generators.  Drop the
code that sets them.

Source/cmGlobalVisualStudio6Generator.cxx

@@ -41,11 +41,8 @@ void cmGlobalVisualStudio6Generator
                  bool optional)
 {
   cmGlobalVisualStudioGenerator::AddPlatformDefinitions(mf);
-  mf->AddDefinition("CMAKE_GENERATOR_CC", "cl");
-  mf->AddDefinition("CMAKE_GENERATOR_CXX", "cl");
   mf->AddDefinition("CMAKE_GENERATOR_RC", "rc");
   mf->AddDefinition("CMAKE_GENERATOR_NO_COMPILER_ENV", "1");
-  mf->AddDefinition("CMAKE_GENERATOR_Fortran", "ifort");
   this->GenerateConfigurations(mf);
   this->cmGlobalGenerator::EnableLanguage(lang, mf, optional);
 }

Source/cmGlobalVisualStudio7Generator.cxx

@@ -27,11 +27,8 @@ void cmGlobalVisualStudio7Generator
 ::EnableLanguage(std::vector<std::string>const &  lang,
                  cmMakefile *mf, bool optional)
 {
-  mf->AddDefinition("CMAKE_GENERATOR_CC", "cl");
-  mf->AddDefinition("CMAKE_GENERATOR_CXX", "cl");
   mf->AddDefinition("CMAKE_GENERATOR_RC", "rc");
   mf->AddDefinition("CMAKE_GENERATOR_NO_COMPILER_ENV", "1");
-  mf->AddDefinition("CMAKE_GENERATOR_FC", "ifort");
   this->AddPlatformDefinitions(mf);
 
   // Create list of configurations requested by user's cache, if any.

Source/cmGlobalXCodeGenerator.cxx

@@ -237,8 +237,6 @@ void cmGlobalXCodeGenerator::EnableLanguage(std::vector<std::string>const&
         cmCacheManager::STRING);
       }
     }
-  mf->AddDefinition("CMAKE_GENERATOR_CC", "gcc");
-  mf->AddDefinition("CMAKE_GENERATOR_CXX", "g++");
   mf->AddDefinition("CMAKE_GENERATOR_NO_COMPILER_ENV", "1");
   if(!this->PlatformToolset.empty())
     {