Driver has a stats infrastructure and all the stats related
commands are using this infrastructure and for this
target_if_mc_cp_stats_stats_event_handler is getting used.
Remove legacy implementation of stats event handler
wma_stats_event_handler and related APIs.
With this change remove unused structures also.
Change-Id: I9a892b5f7486a406654256fc2cc8177f2fafe790
CRs-Fixed: 2481937