Remove barely-used cmMakefile::AddCacheDefinition

The boolean overload of this method was used only to implement option().
We re-implement option() in terms of the main method and removes the
now-unused signature.  This removes some duplicate code that had already
fallen behind on changes (it was not removing the local definition
instead of setting it).

Source/cmMakefile.h

@@ -294,8 +294,6 @@ public:
    * Add bool variable definition to the build. 
    */
   void AddDefinition(const char* name, bool);
-  ///! Add a definition to this makefile and the global cmake cache.
-  void AddCacheDefinition(const char* name, bool, const char* doc);
 
   /**
    * Remove a variable definition from the build.  This is not valid