Remove unused method Family.has_query_api()

Copied from compat by Russell Blau
with commit 3ada8266b67e025a95c4f9d35a38882b84d98cc7,
it was never used according to the Git history.

Moreover, the old MediaWiki query.php API to which has_query_api
refers has been shut down as of 25 August, 2008.

Change-Id: I00d0a8f447b08969820841a190da725bbb00d4bc
Merge "Remove unused method Family.has_query_api()"