Btrfs-progs: remove author and copyright info from man page

Btrfs-progs: remove author and copyright info from man page

>From:
http://man7.org/linux/man-pages/man7/man-pages.7.html
...
AUTHORS lists authors of the documentation or program.Use of
an AUTHORS section is strongly discouraged. Generally,
it is better not to clutter every page with a list of
(over time potentially numerous) authors; if you write
or significantly amend a page, add a copyright notice
as a comment in the source file.  If you are the author
of a device driver and want to include an address for
reporting bugs, place this under the BUGS section.
...

Suggested-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>