NFS: Remove "select RPCSEC_GSS_KRB5

If CONFIG_CRYPTO=n (e.g. arm/shmobile_defconfig):

   WARNING: unmet direct dependencies detected for RPCSEC_GSS_KRB5
     Depends on [n]: NETWORK_FILESYSTEMS [=y] && SUNRPC [=y] && CRYPTO [=n]
     Selected by [y]:
     - NFS_V4 [=y] && NETWORK_FILESYSTEMS [=y] && NFS_FS [=y]

As NFSv4 can work without crypto enabled, remove the RPCSEC_GSS_KRB5
dependency altogether.

Trond says:
> It is possible to use the NFSv4.1 client with just AUTH_SYS, and
> in fact there are plenty of people out there using only that. The
> fact that RFC5661 gets its knickers in a twist about RPCSEC_GSS
> support is largely irrelevant to those people.
>
> The other issue is that ’select’ enforces the strict dependency
> that if the NFS client is compiled into the kernel, then the
> RPCSEC_GSS and kerberos code needs to be compiled in as well: they
> cannot exist as modules.

Fixes: e57d0652 ("NFS & NFSD: Update GSS dependencies")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Suggested-by: Trond Myklebust <trondmy@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>