Disable slow information_schema query that scans all databases and tables.

RT 6639

This query corresponds with bursts of slow queries showing up on ishamel
for s3 and s7 hosts (shards with more wikis and therefore the most tables).
Also slow on special slaves running paritioned tables. Need to find another
way...

Change-Id: I2ac3ed1702cf56274c45f36b9a8bed91a1981625