Remove libmetricslogger dependency from bootstats

Now that bootstats metrics are migrated to statsd in ag/10082348 and in
ag/9957072, we should not need these anymore.(subject to boottime team)

Bug: 147777989
Bug: 148575354
Test: compiles
Change-Id: I00b110dcf5cf4a0fb1673fe05004662b6f3327d0