Looks like they are using Yosemite and up kext signing to lock the file. Try this. command-r boot to recovery then in the Utilities menu launch Terminal and run the command below.
Code:
sudo nvram boot-args=kext-dev-mode=1
That will turn off kext signing protection. Now reboot to regular mode then delete the kext file.
Then command-r boot back to recovery and in Terminal run this command to turn kext signing back on.
It would be a good idea to make a backup before you do this.