SUNRPC: Remove get_mic/verify_mic function pointers from enctype table

SUNRPC: Remove get_mic/verify_mic function pointers from enctype table

Every enctype in the table points .get_mic and .verify_mic at
the same pair of functions. The indirection served no purpose
after the v1 enctype support was removed. Call
gss_krb5_get_mic_v2() and gss_krb5_verify_mic_v2() directly
from the GSS mechanism dispatch and drop the function pointers
from struct gss_krb5_enctype.

Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Anna Schumaker <anna.schumaker@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>