Remove our copy of format_coverage; coverage 0.12.4 includes the fix (#1903)

Author: jcollins-g

pubspec.yaml

@@ -32,7 +32,7 @@ dev_dependencies:
   build: ^1.0.1
   build_runner: ^1.0.0
   build_version: ^1.0.0
-  coverage: any
+  coverage: ^0.12.4
   dhttpd: ^3.0.0
   glob: ^1.1.5
   grinder: ^0.8.2

test/src/utils.dart

@@ -155,8 +155,9 @@ class CoverageSubprocessLauncher extends SubprocessLauncher {
     /// Wait for all coverage runs to finish.
     await Future.wait(currentCoverageResults);
 
-    return launcher.runStreamed(Platform.executable, [
-      'tool/format_coverage.dart', // TODO(jcollins-g): use pub after dart-lang/coverage#240 is landed
+    return launcher.runStreamed('pub', [
+      'run',
+      'coverage:format_coverage',
       '--lcov',
       '-v',
       '-b', '.',