Revert "HAMMERHEAD: Use prebuilt kernel"

This reverts commit c7e7bebd172f12daa1de21b41f3fb4d37ba62065.
hammerhead: switch back to ondemand till slim govenour is back

want to tweak it before we use it on lp again.

Change-Id: I8960ec7a7e25aea5954669df19719d65b031ab2b