MediaMetrics: Cleanup the formatting of session ID

Use the flags Base64.NO_PADDING|Base64.NO_WRAP|Base64.URL_SAFE

This formats the id as one long string without == passing at the end,
Using -_ instead of +/ characters

Bug: 175357495
Test: atest android.media.metrics.cts.MediaMetricsAtomHostSideTests
Change-Id: Iba73976b5677e9a2e5fd3e156a55499005e26904
1 file changed