storaged: emplace recent_perf in load_perf_history_proto

If recent_perf contains existing content, overwrite in method
load_perf_history_proto.  If proto of recent_perf contains a lot of
history, the content would have grown with system_server crashes.

Test: setprop ro.storaged.flush_proto.interval 60
      while true;do sleep 5;stop;sleep 1;start;ps -A|grep storaged;done
      and look at value for rss should remain about 4MB over long term.
Bug: 119798824
Change-Id: I50aae7d61eb791a8fcddbbd829254baf8f708186