releasetools: remove boot.img handling

Depends-on: Ic348d31e8df7933dc4f9f055b7a5a2beacc21d32
http://review.cyanogenmod.org/36813

Change-Id: Ia8dc8219a360c391243dee7a760067277e9e52d1
Merge "releasetools: remove boot.img handling" into cm-10.1
Merge branch 'cm-10.1' into martincz