Fix statsd_test TestOnDumpReportEraseData

After erasing the statsd data, allow statsd to have an empty report, or
even a report with a non-empty metrics wrapper, as long as it doesn't
have any of the former count metrics in it.

Bug: 77909781
Test: make -j8 statsd_test && adb sync data && adb shell data/nativetest64/statsd_test/statsd_test
Change-Id: I525c61aea97a185df8916e4c1b4c4118493ed780