Autoclick Tests: Fix pausing in scroll mode

When pausing autoclick, don't directly call "exitScrollMode()"
because that reverts back to left click.

Demo: http://b/423918214#comment4

Bug: 423918214
Test: atest AutoclickControllerTest
Flag: com.android.server.accessibility.enable_autoclick_indicator
Change-Id: I50e3ef1cd4bb0fb5be3b5c5d22060eaa49cc090e