Removing the line that was resetting the Current deck: field in the

The problem lies in the fact that the local variable ```mCurrentDid``` and the global context ```mCol.getDecks.current()``` are not synchronized. Whenever a card was inserted or any change was made in the activity, the deck in the activity was refreshed to ```mCol.getDecks.current()```. This was weird at least, and annoying at worst : )
After verifying with the desktop application, the behavior after applying this change is the appropriate one.

Also added a comment, just 'cause I feel it's more clear that way!

Regards
Pablo