Remove "Arguments dropped when creating context" logging

Remove "Arguments dropped when creating context" logging

This log was previously reduced from warning to debug.
Cinder removed it entirely in:
https://bugs.launchpad.net/cinder/+bug/1329156

The root cause is this:
Agent heartbeats use an admin context. The context is serialized
with its to_dict method, which exposes 'tenant' and 'project_name'
(These are properties of the class that are calculated from other
attributes). In the controller, this dict is used to initialize a
ContextBase, which does not accept tenant and project_name as arguments,
de facto sending those values as key word arguments.

We can either handle 'tenant' and 'project_name' specially, fix
it any other way, or drop the logging entirely. Is this logging
ever useful?

Change-Id: Ifd51b62bae7b96de44f04836015d2ed939bcb650
Closes-Bug: #1255441