Use Utils.assertTrue() in code that used junit.framework.Assert.assertTrue()

The previous changes to these files, which inlined the behavior
of Assert.assertTrue() were done in a hurry to fix the build.
This change makes use of the existing Utils.assertTrue() method
that was created for this purpose.

Bug: 30188076
Test: make checkbuild
Change-Id: Iacd505f8c3f7cefe6de94d30b56e39600bb9b0af