- did some cleanup on p_mobj.cpp

* deleting some unused code
* turned several class methods into static local functions in cases where they never were used outside this file.
* inlined the dangerous assignment operator in the only place where it was used.

src/common/objects/dobject.cpp

@@ -515,5 +515,4 @@ void *DObject::ScriptVar(FName field, PType *type)
 	}
 	// This is only for internal use so I_Error is fine.
 	I_Error("Variable %s not found in %s\n", field.GetChars(), cls->TypeName.GetChars());
-	return nullptr;
 }