remove restart upgrade wizard menu entry

As per issue [1722](https://code.google.com/p/ankidroid/issues/detail?id=1722), this commit removes the "restart upgrade process menu" item. Suggest including in **version 2.1** since this item may confuse some users who think it will *upgrade the application*... it also clogs up the menu for 99% of users. 

The upgrade wizard itself is left intact, so the minority of users updating from 1.x can still upgrade their decks automatically, they just can't restart the upgrade wizard if it fails, meaning they have to either follow the manual upgrade instructions, or rollback to version 2.0.4.