xfrm: delete xfrm4_output_finish xfrm6_output_finish declarations

These function declarations are not needed any more.
The definitions were deleted.

Fixes: 2ab6096d ("xfrm: remove output_finish indirection from xfrm_state_afinfo")
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>