Remove the query cache and all code related to it. Note that the SQL_NO_CACHE
keyword stays, but now does nothing (not even semantic checking that it's not
in subqueries).

In the process, we set HAVE_QUERY_CACHE to NO, so that interested clients can
test for it reliably.

NDB code has not been removed but commented out for later cleanup, at the
request of the NDB team.

Change-Id: I0aa54211dbcccca1f408c01aa91b58e33c39294e