Remove executable files.

Remove executable files.
These files are for a legacy updating system. This updating system would only apply to users who have not used youtube-dl for at least a year (because if they did use it, they would notice that basically everything about every service, maybe except a couple of YouTube videos, has changed in between).
We often get commits including these files, and they are irritating for us core developers as well. Good riddance!
If anyone notes that their updates fail, they can just reinstall (see http://rg3.github.io/youtube-dl/download.html for instructions).