xprtrdma: Remove transfertypes array

Clean up: This array was used in a dprintk that was replaced by a
trace point in commit ab03eff5 ("xprtrdma: Add trace points in
RPC Call transmit paths").

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>