draft-2 support: fix or remove?

[mr-c]

sometime in the last month (it's been that long since we had a new release) cwltool no longer works with draft-2:

https://ci.commonwl.org/job/cwltool-conformance/290/console

Shall we fix it or remove it?

[mr-c]

git bisect on schema_salad shows the breakage for draft-2 was introduced in common-workflow-language/schema_salad@8a6eaff

[mr-c]

I removed draft-2 support from the conformance tests so we should proceed with removing it from the reference implementation.

[kapilkd13]

Is there some organization who still have workflows that use draft-2.

[anton-khodak]

Closed in #520