MAINTAINERS: remove duplicate bug filling description

I have noticed that two different descriptions for B: entries in
MAINTAINERS were merged: commit 686564434e88 ("MAINTAINERS: Add bug
tracking system location entry type") and 2de2bd95f456 ("MAINTAINERS:
add "B:" for URI where to file bugs").

This patch keeps the description from 2de2bd95f456.  There has been a
discussion [1] about whether this more detailed description is useful
and what it exactly implies.  I find it more useful and general, and the
author of 686564434e88 agreed in the end that either is fine.

[1] https://lkml.org/lkml/2016/12/8/71

Link: http://lkml.kernel.org/r/20161219085158.12114-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -81,7 +81,6 @@ Descriptions of section entries:
 	Q: Patchwork web based patch tracking system site
 	T: SCM tree type and location.
 	   Type is one of: git, hg, quilt, stgit, topgit
-	B: Bug tracking system location.
 	S: Status, one of the following:
 	   Supported:	Someone is actually paid to look after this.
 	   Maintained:	Someone actually looks after it.