[flow][tests] Remove call_type test suite

Summary:
This is the test suite for $Call. I don't think there is any value leftover in this suite after $Call support is deleted, since what's being tested doesn't map to conditional type, so I will just delete it now.

- test.js: very simple tests, the arity error doesn't map to conditional type
- union.js: mostly testing union function call behavior, doesn't map to anything in conditional type
- intersection.js: doesn't make sense in conditional type

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D62783714

fbshipit-source-id: 3932acc8a4c70add210fc8cc52ac1ecbb7efe02e