Fix flaky fail of ApplicationsStateRoboTest

The flaky fail of ApplicationsStateRoboTest is affected by that we added
a thread mechanism to load the app icon in the AppEntry constructor
which is to improve the scrolling of App info page. There will have a
default app icon if the thread finish before icon null assertion.

In the latest design, the app icon null assertion is not required,
therefore remove them to fix test fail.

Fixes: 159402083
Test: robotests
Change-Id: If2577292a42c653ae3c7bebe9392f4fb62365a44