Remove unsupported warning for OpenAPI 3.1

[kylef]

Removes the warning

Version '3.1.0' is not fully supported

Depends on:

• Add missing warnings for unsupported OpenAPI 3.1 functionality #603
• Add unsupported warnings for OpenAPI 3.1 schema #602
• Support OpenAPI 3.1 Schema Object const #601
• Support array of type in Schema Object #600
• Include nullable with Schema Object without a type on OAS 3.1 #599

and one more un-pushed change. Once these are wrapped up, all the unsupported 3.1 behaviours will have their own warning messages, or the functionality should be functional.

[opichals]

LGTM