staging: r8188eu: remove unused parameter

All callers of rtl8188eu_xmitframe_complete set the pxmitbuf parameter to
NULL, in which case rtl8188eu_xmitframe_complete allocates another
xmit_buf internally.

Remove the pxmitbuf parameter and resulting dead code.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20221230180646.91008-6-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>