SUNRPC: Drop redundant CONFIG_ from CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES

The "CONFIG_" portion is added automatically, so this was being expanded
into "CONFIG_CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES"

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>