Cleanup in ExpandableNotificationRowTest

After adding some new test cases to ExpandableNotificationRowTest we
have noticed an increasing number of leaks of ExpandableNotificationRow.

How did this happen:
 - Mockito was holding onto some ExpandableNotificationRow instances and resetting the inline mocks didn't help to release them
 - NotificationTestHelper has a mock StatusBarStateController
 - NotificationTestHelper creates a real HeadsUpManagerPhone passing in
   the mock StatusBarStateController
 - HeadsUpManagerPhone sets a listener on the mock StatusBarStateController
 - that listener holds onto a NotificationEntry
 - that entry has an ExpandableNotificationRow

This CL:
 - uses a mock HeadsUpManagerPhone
 - removes some unnecessary ExpandableNotificationRow instances from ExpandableNotificationRowTest

Fixes: 265135790
Test: create heap dumps using com.android.systemui.MemoryTrackingTestCase and compare them with go/ahat
Test: atest ExpandableNotificationRowTest
Test: atest SystemUITests

Change-Id: I314a1f6e59f095f8cc6018e3d65bf90bd9cd4a75
Merged-In: I314a1f6e59f095f8cc6018e3d65bf90bd9cd4a75