Revert "fix: enable IAM auth for custom types (#2961) (#2971)"

[palpatim]

This reverts commit 0e003d2.

Description of changes

The previous commit (#2971, which re-enables #2961) introduces a behavior that automatically annotates a custom type with @aws_iam if enableIamAuthorizationMode is true.

This breaks customer schemas who rely on AppSync's default authorization mode to authorize custom types. E.g., the following scenario:

• Default authorization mode: Cognito User Pools
• Enable IAM Authorization: true
• Schema

  type Foo {
    bar: String
    baz: Int
  }
  
  type Query {
    getFoo: Foo
      @auth(rules: [{ allow: private }])
      @function(name: "foofunction")
  }

We must not re-merge this change until we have better test coverage of all the use cases and edge cases that this could impact.

Issue #, if available

• Original issue: IAM not authorized for custom types if default auth mode is not IAM #2929
• Initial PR merge: fix: enable IAM auth for custom types #2961
• First revert: Revert "fix: enable IAM auth for custom types (#2961)" #2964
• Re-commit: fix: re-enable IAM auth for custom types (#2961) #2971

Checklist

• PR description included

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.