libmetricslogger: Use libBionicGtestMain instead of a custom test runner.

Also remove commented out code I accidentally left in.

Bug: 34456830
Test: libmetricslogger_test
Change-Id: If76d3013ec7eaa71cef67c6db04d810745e3833e
diff --git a/libmetricslogger/Android.bp b/libmetricslogger/Android.bp
index ca8af57..75eab66 100644
--- a/libmetricslogger/Android.bp
+++ b/libmetricslogger/Android.bp
@@ -57,8 +57,8 @@
         "libbase",
         "libmetricslogger_debug",
     ],
+    static_libs: ["libBionicGtestMain"],
     srcs: [
         "metrics_logger_test.cpp",
-        "testrunner.cpp",
     ],
 }