Enable unit tests for some utils in postsubmit

Enabled unit tests for hevcUtils, ExtractorFactory and TimedText in
postsubmit.

These were marked as dynamic-presubmit and those are now
changed to postsubmit as these tests now use DynamicConfig.xml and
can download the required files without any extra arguments.

After some time of running these in postsubmit, these will be changed
to presubmit.

Bug: 304383609
Test: atest ExtractorFactoryTest HEVCUtilsUnitTest TimedTextUnitTest
Change-Id: I934849f82062eac04f4fb988c1bf200fb434d815