Merge libstatspush_compat and libstatssocket_q

This cleanup makes it clear that there are only two acceptable ways of
logging to the socket: either through libstatspush_compat or
libstatssocket (which will soon be renamed to libstatspush).

Test: m -j
Change-Id: I6a49b4995b56df462e1be901ea5e54acfe2e8bac