[ Device Lab ] Upgrade Device Lab projects to Java 18 (#165987)

Should resolve issues related to the following messages being output on
stderr:

```
warning: [options] source value 8 is obsolete and will be removed in a future release"
warning: [options] target value 8 is obsolete and will be removed in a future release
warning: [options] To suppress warnings about obsolete options, use -Xlint:-options.
```

Fixes https://github.com/flutter/flutter/issues/165973

dev/devicelab/lib/tasks/run_tests.dart

@@ -105,12 +105,6 @@ class AndroidRunOutputTest extends RunOutputTask {
     }
   }
 
-  @override
-  bool isExpectedStderr(String line) {
-    // TODO(egarciad): Remove once https://github.com/flutter/flutter/issues/95131 is fixed.
-    return line.contains('Mapping new ns');
-  }
-
   @override
   TaskResult verify(List<String> stdout, List<String> stderr) {
     final String gradleTask = release ? 'assembleRelease' : 'assembleDebug';