Don't explicitly launch test activity in fullscreen in AssistantStackTests
This is a partial revert of aosp/1442704.
With aosp/1473879, the tests take the default display windowing
mode into account when asserting the windonwing mode of the test
activity, but we still forcefullly launch them in fullscreen in
some places (introduced by aosp/1442704), so they contradict with
each other.
Bug: 190327854
Test: AssistantStackTests
Change-Id: I9661e6ef54bcb6709cfe1e8ca15c032c804db970
(cherry picked from commit 152360e7bf5c51ba16f4d1e07701a69575255d06)
2 files changed
