Disable the schema-linter until I can fix problems with it.
Disable the schema-linter until I can fix problems with it.

I know that the hack we're using to deal with external interfaces
isn't very good.  Now it's turned up real problems.  Disable for now.

Issues: https://khanacademy.slack.com/archives/CJSE4TMQX/p1585078347067000

Auditors: benkraft, jvoll

Test plan:
In webapp: ka-lint services/assignments/schema.graphql

Khan/khan-linter,Khan/khan-linter,Khan/khan-linter,Khan/khan-linter