Originally by Christoph Hellwig back in February.
It recieved no objections when posted to l-k & Jens.

o remove DEVICE_REQUEST definitions - never used in blk.h itself.
o remove DEVICE_ON() - never used at all.
o define LOCAL_END_REQUEST when we do not want end_request() instead
  of other hacks.
o remove DEVICE_OFF() - only used in floppy driver, thus one now has
  a private end_request().
o use private end_request() functions for drivers not providing
  randomness.
o remove TIMEOUT_VALUE - only ever used in hd.c