cdx: remove unused struct 'cdx_mcdi_copy_buffer'

'cdx_mcdi_copy_buffer' has been unused since the original
commit eb96b740192b ("cdx: add MCDI protocol interface for firmware
interaction").

Looking at lkml, it was used in the V1 posting but was removed
somewhere before V6.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <[e-mail]>
Acked-by: Nipun Gupta <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/cdx/controller/mcdi.c

···
 #include "bitfield.h"
 #include "mcdi.h"
 
-struct cdx_mcdi_copy_buffer {
-	struct cdx_dword buffer[DIV_ROUND_UP(MCDI_CTL_SDU_LEN_MAX, 4)];
-};
-
 static void cdx_mcdi_cancel_cmd(struct cdx_mcdi *cdx, struct cdx_mcdi_cmd *cmd);
 static void cdx_mcdi_wait_for_cleanup(struct cdx_mcdi *cdx);
 static int cdx_mcdi_rpc_async_internal(struct cdx_mcdi *cdx,