dp_tx_pdev_detach API takes care of flushing
tx descriptors and multicast enhancement mem
cleanup
dp_pdev_deinit takes care of cleaning up the
above actions and dp_tx_pdev_detach is simply
a redundant piece of code
Hence remove dp_tx_pdev_detach API and call
dp_tx_desc_flush directly from dp_pdev_deinit
CRs-Fixed: 2769303
Change-Id: Ic798793e81eefc7dc905ca7552fdca13e9fddd8c