Remove enableSiteLinkWidget setting in the client

This is true by default, and has been for a while
and true, as used on wikimedia sites.

The setting was introduced when the widget was introduced,
just in case there were performance issues and it had to
be disabled. No need for the setting now and makes
things over complex.

Change-Id: I5e143dbba00dc524ce412c3ab6abd53abbd90226
Merge "Remove enableSiteLinkWidget setting in the client"