GPU Python: Use string literals in shader.from_builtin and shader.code_from_builtin.

Also, the gpu.shader.builtin submodule becomes obsolete, so it has been removed.

source/blender/python/gpu/gpu_py_api.c

@@ -63,7 +63,6 @@ static struct PyModuleDef GPU_module_def = {
 PyObject *BPyInit_gpu(void)
 {
 	PyObject *sys_modules = PyImport_GetModuleDict();
-	PyObject *subsubmodule;
 	PyObject *submodule;
 	PyObject *mod;
 
@@ -81,8 +80,5 @@ PyObject *BPyInit_gpu(void)
 	PyModule_AddObject(mod, "shader", (submodule = BPyInit_gpu_shader()));
 	PyDict_SetItem(sys_modules, PyModule_GetNameObject(submodule), submodule);
 
-	PyModule_AddObject(submodule, "builtin", (subsubmodule = BPyInit_gpu_shader_builtin()));
-	PyDict_SetItem(sys_modules, PyModule_GetNameObject(subsubmodule), subsubmodule);
-
 	return mod;
 }