MediaMetrics: Change dumpsys format

As the dumpsys no longer needs to be parseable by a program
convert to a more human readable form.

1) Make default time REALTIME consistently.
2) Dump time as a human readable string.
3) Remove dumpsys versioning code.
4) Delimiter changes.

Test: atest mediametrics_tests
Test: adb shell dumpsys media.metrics
Bug: 138583596
Change-Id: I6ee7d81a18e0e220b258c722d232c05805118abb