[pvr.hts] Improve sync after connection restore.

tvheadend may running (on another server) while xbmc is suspended. In case timers/recordings/channels/tags are modified while xbmc is not active and xbmc gets resumed, it will not handle timers/recordings/... deleted meanwhile in tvheadend. This PR fixes this issue.
Okay, willr emove the mutex stuff. 

Clearing the arrays and refetching new data is the actual goal, resetting the arrays is a rollback in case somethings goes wrong with enableasync call. The old data are just old, not completely wrong. Idea is to have at least someting in case enableasynv goes wrong