wear_ui: Remove dead 'self' and 'progress_t'.

They were once used for progress_thread() that's pthread_create'd by
WearRecoveryUI::Init(). They have become dead since the removal of
progress_thread() (commit ad8b5a6c).

Also add the missing include of <pthread.h> for pthread_mutex_lock().

Test: lunch a watch target and `m recoveryimage`.
Change-Id: I748cf4511434ac4ce97dddf89b0e42e68a5da04b