change log recovery to generic device_recovery_start function

Remove (or at least stop calling) the HTC-specific mechanism for
preserving the recovery log from before a radio or hboot update.
Replace it with a generic device_recovery_start() function which each
device's code can implement to do whatever it wants on recovery
startup.

Change-Id: If3cca4b498c0b1cf0565236404ecf56a1fc46123