Refactor how script api reads current mod name

This is to prevent future mistakes and make it clearer whether
the mod name can be trusted depending on how it is retrieved.

src/script/lua_api/l_client.h

@@ -60,12 +60,6 @@ class ModApiClient : public ModApiBase
 	// gettext(text)
 	static int l_gettext(lua_State *L);
 
-	// get_last_run_mod(n)
-	static int l_get_last_run_mod(lua_State *L);
-
-	// set_last_run_mod(modname)
-	static int l_set_last_run_mod(lua_State *L);
-
 	// get_node(pos)
 	static int l_get_node_or_nil(lua_State *L);