Mediaserver memory increase after record

mediaserver pss memory in meminfo cat by 'adb shell dumpsys meminfo mediaserver'
will increase after memory leak test. The test will record many times using front
and back camera.
we found mediametrics::Item been create but not been deleted when do video record,
witch will cause memory leak. We should always delete it if mMetricsItem not NULL.

Bug: 174438149
Change-Id: I45e5a7918f032058fd76023c2ca4d82881e8f9d1