Fix multiple Java warnings (#6201)

wpilibjIntegrationTests/src/main/java/edu/wpi/first/wpilibj/test/TestBench.java

@@ -52,6 +52,7 @@ public final class TestBench {
   public static final int DIOCrossConnectA1 = 6;
 
   /** The Singleton instance of the Test Bench. */
+  @SuppressWarnings("unused")
   private static TestBench instance = null;
 
   /**

wpilibjIntegrationTests/src/main/java/edu/wpi/first/wpilibj/test/TestSuite.java

@@ -50,7 +50,10 @@ public class TestSuite extends AbstractTestSuite {
     TestBench.out().println("Starting Tests");
   }
 
+  @SuppressWarnings("unused")
   private static final Logger WPILIBJ_ROOT_LOGGER = Logger.getLogger("edu.wpi.first.wpilibj");
+
+  @SuppressWarnings("unused")
   private static final Logger WPILIBJ_COMMAND_ROOT_LOGGER =
       Logger.getLogger("edu.wpi.first.wpilibj.command");