[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.
I guess this works without crashing because nothing else can write to these members when OnConnectionRestored() is called. what are you trying to do here by first clearing and then resetting the arrays?