exit/bdflush: Remove the deprecated bdflush system call

The bdflush system call has been deprecated for a very long time.
Recently Michael Schmitz tested[1] and found that the last known
caller of of the bdflush system call is unaffected by it's removal.

Since the code is not needed delete it.

[1] https://lkml.kernel.org/r/36123b5d-daa0-6c2b-f2d4-a942f069fd54@gmail.com
Link: https://lkml.kernel.org/r/87sg10quue.fsf_-_@disp2133
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

include/uapi/linux/capability.h

@@ -243,7 +243,6 @@ struct vfs_ns_cap_data {
 /* Allow examination and configuration of disk quotas */
 /* Allow setting the domainname */
 /* Allow setting the hostname */
-/* Allow calling bdflush() */
 /* Allow mount() and umount(), setting up new smb connection */
 /* Allow some autofs root ioctls */
 /* Allow nfsservctl */