ipalib: move server-side plugins to ipaserver

Move the remaining plugin code from ipalib.plugins to ipaserver.plugins.

Remove the now unused ipalib.plugins package.

https://fedorahosted.org/freeipa/ticket/4739

Reviewed-By: David Kupka <dkupka@redhat.com>

ipalib/__init__.py

@@ -908,10 +908,8 @@ class API(plugable.API):
     @property
     def packages(self):
         if self.env.in_server:
-            import ipalib.plugins
             import ipaserver.plugins
             result = (
-                ipalib.plugins,
                 ipaserver.plugins,
             )
         else: