locking/Documentation: Remove stale crossrelease_fullstack parameter

locking/Documentation: Remove stale crossrelease_fullstack parameter

The cross-release lockdep functionality has been removed in:

   e966eaeeb623: ("locking/lockdep: Remove the cross-release locking checks")

... leaving the kernel parameter docs behind. The code handling
the parameter does not exist so this is a plain documentation change.

Signed-off-by: David Sterba <dsterba@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: byungchul.park@lge.com
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20180108152731.27613-1-dsterba@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>