pixelstat: MM metrics: keep 1st report

For atom 'PixelMmMetricsPerHour', previously we skip the first round
metrics reports.  The intention was to skip those heavy boot-time metrics
so that it won't affect our statistics on normal data.

However, in newer implementation, we already have the
elapsed_timetsamp_nanos field (event time in "devices time since boot"
format) in the Suez table (b/223529199).  Now it's even better:

We can use the device time to filter out those boot events, and we
can separate the statistics into two categories:  (1) normal, and
(2) boot time.

So this time we don't skip the first round report.

Test: n/a
Bug: 234564667
Signed-off-by: Robin Hsu <robinhsu@google.com>
Change-Id: I05705e4b16b6e790b54b17a149179b6ea24f2fdf