Remove SQL Hints from Activities class

[zippykid]

This ticket is the result of a discussion here: http://buddypress.org/support/topic/performance-issues-with-the-wp_bp_activities-table/

Basically, I think it would be good if the SQL hint should be removed from the query in the activities class that returns a COUNT() .

Some tests and results of EXPLAIN are provided here; ​https://gist.github.com/vidluther/9370018

[boonebgorges]

Thanks, zippykid.

[boonebgorges]

In 8071:

Streamline COUNT query in BP_Activity_Activity::get

It's unnecessary to use an ORDER BY clause when counting, and the index hint
was doing more harm than good, especially in cases where a specific ID was
passed.

See #5448

[boonebgorges]

OK, the index hint is removed from the count query. I think we probably should remove it from the other query as well, but this is something I can't investigate right now, so I'm going to move this ticket to the next milestone so there's more time for benchmarking and testing.

[boonebgorges]

There's no index hint in use in either place anymore.