Unskip required attribute tests for input().

Add missing required attribute/classname conventions and remove lengthy
tests.
Remove redundant test.

This test is redundant as the create/update logic is part of the context
classes now.
Remove redundant test.

This test serves no purpose now. With input methods reasonably
idempotent we don't need tests like this.
Remove more redundant tests.

* Remove redundant tests around detecting required attribute.
* Remove test that didn't actually do anything special.
Fix previously skipped test.
Fix typo.
Remove option that no longer works.
Merge pull request #2905 from markstory/3.0-formhelper-test-cleanup

3.0 formhelper input() required attribute