MediaMetrics: Remove remaining BOOTTIME references

Use SYSTEM_TIME_REALTIME instead.
As we always specify the time when the item arrives,
this has no real effect, just for internal consistency.

Test: atest mediametrics_tests
Bug: 149850236
Change-Id: I34d7bed0c4e25b288493ce1ecf3574c4d87334d9
2 files changed