Don't remove widget providers when whitelist changes.

When a widget provider is removed from the whitelist
of widgets that work across profiles just remove the
currently bound widgets don't remove the provider.
This allows the provider to be added back to the whitelist
or to be used from widget hosts within the profile.

Bug: 21180997
Change-Id: I5d3a81fb088092b65cc4e8e158be4a292c5c8288