Remove localtime_tz and strftime_tz.

This also brings our copy of strftime.c much closer to upstream, though
we still have several GNU extensions and hacks to deal with Android32's
broken time_t.

Bug: 15765976

(cherry picked from commit 39d903ae)

Change-Id: Ie278d3e976b7adc77bad5ce795dd4899cfbf3648