Make equals() and hashCode() final on Subject.

Fixes google#247
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125528464

core/src/main/java/com/google/common/truth/Subject.java

@@ -361,7 +361,7 @@ protected void failWithRawMessage(String message, Object... parameters) {
  */
  @Deprecated
  @Override
- public boolean equals(@Nullable Object o) {
+ public final boolean equals(@Nullable Object o) {
  throw new UnsupportedOperationException(
  "If you meant to test object equality, use .isEqualTo(other) instead.");
  }
@@ -372,7 +372,7 @@ public boolean equals(@Nullable Object o) {
  */
  @Deprecated
  @Override
- public int hashCode() {
+ public final int hashCode() {
  throw new UnsupportedOperationException("Subject.hashCode() is not supported.");
  }
 }