Deprecate old PID classes (#1964)

PIDBase was only used by the old PIDController, which is deprecated.
PIDInterface is only used by PIDBase, and that's deprecated by this
commit.

wpilibj/src/main/java/edu/wpi/first/wpilibj/PIDBase.java

@@ -26,7 +26,10 @@ import static edu.wpi.first.wpilibj.util.ErrorMessages.requireNonNullParam;
  * <p>This feedback controller runs in discrete time, so time deltas are not used in the integral
  * and derivative calculations. Therefore, the sample rate affects the controller's behavior for a
  * given set of PID constants.
+ *
+ * @deprecated All APIs which use this have been deprecated.
  */
+@Deprecated(since = "2020", forRemoval = true)
 @SuppressWarnings("PMD.TooManyFields")
 public class PIDBase implements PIDInterface, PIDOutput, Sendable, AutoCloseable {
   public static final double kDefaultPeriod = 0.05;

wpilibj/src/main/java/edu/wpi/first/wpilibj/PIDInterface.java

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2016-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2016-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -7,6 +7,7 @@
 
 package edu.wpi.first.wpilibj;
 
+@Deprecated(since = "2020", forRemoval = true)
 @SuppressWarnings("SummaryJavadoc")
 public interface PIDInterface {
   @SuppressWarnings("ParameterName")