[PATCH] list_del-debug fix

These two BUG_ON()s are redundant and undesired: we're checking for this
condition further on in the function, only better.

Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>