VS: Set CMAKE_VS_PLATFORM_NAME for VS7 and VS71 too

Move the code which sets CMAKE_VS_PLATFORM_NAME from
cmGlobalVisualStudio8Generator to cmGlobalVisualStudio7Generator.

Source/cmGlobalVisualStudio8Generator.h

@@ -30,8 +30,6 @@ public:
   ///! Get the name for the generator.
   virtual const char* GetName() const {return this->Name.c_str();}
 
-  const char* GetPlatformName() const;
-
   /** Get the documentation entry for this generator.  */
   static void GetDocumentation(cmDocumentationEntry& entry);
 
@@ -87,7 +85,6 @@ protected:
                                    const char* path, cmTarget &t);
 
   std::string Name;
-  std::string PlatformName;
   std::string WindowsCEVersion;
 
 private: