Use java.util.Objects instead on internal API

Not needed since java.util.Objects implements all the needed
functionality.

Change-Id: Icd31d49a9801d1705427f028e9ac927d58e7d34c

Conflicts:
	services/java/com/android/server/am/ActivityStack.java

Conflicts:
	services/java/com/android/server/am/ActivityStack.java