sysctl: ipv4 remove binary sysctl paths where they are broken

Currently tcp_available_congestion_control does not even attempt being read
from sys_sysctl, and ipfrag_max_dist while it works allows setting of invalid
values using sys_sysctl.

So just kill the binary sys_sysctl support for these sysctls.  If the support
is not important enough to test and get right it probably isn't important
enough to keep.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alexey Dobriyan <adobriyan@sw.ru>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>