Revert "[ Device Lab ] Upgrade Device Lab projects to Java 18" (#166016)

Reverts flutter/flutter#165987

Reason for revert: multiple gradlew failures on devicelab tests

dev/devicelab/lib/tasks/run_tests.dart

@@ -105,6 +105,12 @@ 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';