Stop cloning timelib_tzinfos

Summary: They're readonly, and we keep a cache of them, so just
use the cached ones.

Reviewed By: @jdelong

Differential Revision: D1689771
Fix leak in tvCoerce*

Summary: We cant delete DeleteUnwinderExceptions

Reviewed By: @jdelong, @edwinsmith, @swtaarrs

Differential Revision: D1690785