befs: remove check for CONFIG_BEFS_RW

Befs contains a check for CONFIG_BEFS_RW for over a decade now. The
related Kconfig symbol never existed, so this check always evaluated to
true. Remove it.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>