All tests should use schema 2 instead of schema 1 manifests

We'll be disabling support for schema 1 manifest on January 22, 2021. Before that, we need to change all tests (a lot of them) that are currently using schema 1 manifests (more prominently the API integration tests). These should either use schema 2 manifests or be removed if they're meaningless for other manifests besides schema 1.

Alternatively, we can do this in two steps:

1. Disable support for schema 1 manifests at the API level but continue to use them internally for test purposes;
2. After a while, convert schema 1 tests to schema 2 and remove schema 1 source code.

This is probably the safest option.