MediaMetrics: Minor logging fixes

Remove extraneous right brace in Time Machine dump.
Do not suppress repeated EVENT properties in the Time Machine.
Use "--" prefix instead of "-" for long dumpsys argv options.

Test: atest mediametrics_tests
Test: adb shell dumpsys media.metrics
Bug: 138583596
Change-Id: I874be909ac08641b14dd12fb2c83de7a276a1796