Remove kernel-headers apt-get call

Kernel-headers is no longer necessary since it's
installed by devstack_gate.sh script. This will
also add support to Fedora and other distros
once apt-get isn't being called anymore.

Change-Id: I36b9a126a62a0c80562b0c22a94af3ce08a9008e
Merge "Remove kernel-headers apt-get call"