nfs-utils: remove disabled code from support/nfs/rpcmisc.c

After some recent discussions, we want to rely on the kernel's network
layer to autotune socket buffers.  Since this code is already disabled in
support/nfs/rpcmisc.c (and has been for some time), let's just remove it.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>