Remove CONFIG_STACK_BACKTRACE_COLS.

This feature didnt work out: instead of making kernel debugging more
efficient, it produces much harder to read stacktraces!  Check out this trace
for example:

  http://static.flickr.com/47/158326090_35d0129147_b_d.jpg

That backtrace could have been printed much nicer as a one-entry-per-line
thing, taking the same amount of screen real-estate.

Plus we remove 30 lines of kernel code as well.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>