Remove prefix bytes

[icambron]

This is a "fix" for #18. I suspect it's wrong.

I couldn't get Chrome to accept my extension. I noticed that the CRXs that Chrome generates have 296-byte keys, but crxmake generates 316-byte keys because it tacks 22 bytes to the front of the key I provided. I removed the code that does that and now my extension works.

I suspect what's happening is that my key is coming with the right ceremonial prefix in it, but that crxmake isn't recognizing it as "correct" and thus tacking on its own, thereby breaking things. Perhaps my fix breaks other things, such as keys generated by crxmake itself (I didn't try it). I don't really know how this stuff works, what the prefix really does, or why it would be constant (seems a bit odd).

[cielavenir]

That's quite strange. This code (modified crxmake) is working flawlessly.
https://github.com/cielavenir/ctouch/blob/master/support/crx.rb