Revert^2 "[metrics] Add StatsdBackend"

Adds a new backend that allows reporting ART's metrics to statsd, where
they can then be uploaded to Westworld.

Manual Testing Instructions:

Run the following commands.

    m statsd_testdrive
    adb shell setprop dalvik.vm.extra-opts              \
                      -Xwrite-metrics-to-statsd\\\      \
                      -Xwrite-metrics-to-log\\\         \
                      -Xmetrics-reporting-period=10
    adb shell stop && adb shell start
    statsd_testdrive 332

After about a minute, you should see several atoms logged from ART.

This reverts commit dbad1ef673140c66cdbcbbf40424674ae8e2b4c8.
Reason for revert: Added statsd apex to prebuilts

Bug: 178236337
Test: Manual, see above
Test: see instructions on https://r.android.com/1591932
Change-Id: I2071983c04c51efe88df6a56c59fc418fe6e9424
diff --git a/runtime/runtime_options.def b/runtime/runtime_options.def
index 1961113..9552d50 100644
--- a/runtime/runtime_options.def
+++ b/runtime/runtime_options.def
@@ -186,8 +186,9 @@
 // This is to enable/disable Perfetto Java Heap Stack Profiling
 RUNTIME_OPTIONS_KEY (bool,                PerfettoJavaHeapStackProf,      false)
 
-// Whether to dump ART metrics to logcat
+// Metrics configuration settings
 RUNTIME_OPTIONS_KEY (Unit,                WriteMetricsToLog)
+RUNTIME_OPTIONS_KEY (Unit,                WriteMetricsToStatsd)
 RUNTIME_OPTIONS_KEY (std::string,         WriteMetricsToFile)
 RUNTIME_OPTIONS_KEY (Unit,                DisableFinalMetricsReport)
 RUNTIME_OPTIONS_KEY (unsigned int,        MetricsReportingPeriod)