core.common: move away import related stuff to my.core.utils.imports

moving without backward compatibility, since it's extremely unlikely they are used for any external modules

in fact, unclear if these methods still have much value at all, but keeping for now just in case

my/demo.py

@@ -23,7 +23,7 @@ class demo(user_config):
     def external_module(self):
         rpath = self.external
         if rpath is not None:
-            from .core.common import import_dir
+            from .core.utils.imports import import_dir
             return import_dir(rpath)
 
         import my.config.repos.external as m # type: ignore