[dev] do not import distributed and graphbolt when import dgl (#7676)

Author: Rhett-Ying

python/dgl/__init__.py

@@ -62,6 +62,3 @@
 from .mpops import *
 from .homophily import *
 from .label_informativeness import *
-
-if backend_name == "pytorch":
-    from . import distributed