Drop builtin command documentation

Drop all GetTerseDocumentation and GetFullDocumentation methods from
commands.  The command documentation is now in Help/command/*.rst files.

Source/cmFindFileCommand.h

@@ -35,17 +35,7 @@ public:
     }
   virtual const char* GetName() const { return "find_file";}
 
-  /**
-   * Succinct documentation.
-   */
-  virtual const char* GetTerseDocumentation() const
-    {
-    return "Find the full path to a file.";
-    }
-
   cmTypeMacro(cmFindFileCommand, cmFindPathCommand);
-protected:
-  virtual void GenerateDocumentation();
 };