qcacmn: Remove RX_BUFFER_SIZE from dp_rx.h to fix compilation
RX_BUFFER_SIZE macro got introduced by mistake during rebase. The macro
is present in hal_rx.h. Removing the extra macro.
CRs-Fixed: 2382076
Change-Id: Ia66079d6d4543b4e3fd99e9f0c0376353a92aa9c