Documentation: befs.txt: no maintainer, orphaned

Remove the name of Sergey Kostyliov as maintainer of befs.
In the MAINTAINERS file, befs is orphaned.

Signed-off-by: Marcos Souza <marcos.mage@gmail.com>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>