NFS: Don't enable NFS v2 by default

This came up during one of the Bake-a-thon discussions. NFS v2 support
was dropped from nfs-utils/mount.nfs in December 2021. Let's turn it
off by default in the kernel too, since this means there isn't a way
to mount and test it.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Reviewed-by: Jeffrey Layton <jlayton@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>