tools/liblockdep: Use the rbtree header provided by common tools headers

tools/liblockdep: Use the rbtree header provided by common tools headers

Recent changes to rbtree.h may break compilation. There is no
reason to use a liblockdep specific header to begin with, so
we'll use the one shared with all other tools/.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1440479985-6696-3-git-send-email-sasha.levin@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>