[PATCH] md: complete conversion of md to use kthreads

[PATCH] md: complete conversion of md to use kthreads

There are a few loose ends following the conversion of md to use kthreads:

- Some fields in mdk_thread_t that aren't needed (kthreads does it's own
  completion and manages it's own name).

- thread->run is now never NULL, so no need to check

- Some tests for signal_pending that aren't needed (As we don't use signals
  to stop threads any more)

- Some flush_signals are not needed

- Some waits are interruptible and don't need to be.

Signed-off-by: Neil Brown <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>