RDMA/rxe: Remove reliable datagram support

The rdma_rxe driver does not actually support the reliable datagram
transport but contains a variable with RD opcodes in driver code.  And
this variable is never used. So remove it.

Link: https://lore.kernel.org/r/20221112023537.432912-1-yanjun.zhu@intel.comSigned-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_hdr.h

@@ -742,7 +742,6 @@ enum aeth_syndrome {
 	AETH_NAK_INVALID_REQ	= 0x61,
 	AETH_NAK_REM_ACC_ERR	= 0x62,
 	AETH_NAK_REM_OP_ERR	= 0x63,
-	AETH_NAK_INV_RD_REQ	= 0x64,
 };
 
 static inline u8 __aeth_syn(void *arg)