include/rxrpc/types.h: Remove unused header

The header file include/rxrpc/types.h does not seem to be used
anywhere. It was orphaned by 63b6be55 "[AF_RXRPC]: Delete the old
RxRPC code.". Remove it.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>