Convert IntegratedDownloadsUiTest to Junit 4

This class isn't being ran at the moment. Let's convert it first and
revisit it once all files have been converted. This migrates usages of
Suppress to Ignore as well.

Bug: 407646510
Test: NONE
Flag: EXEMPT test change
Change-Id: I15e1cba269108d46ee85a234203d20bf0eab9811