Fix usage of "not"

Constructs such as:

type: object
not:
  type: object

will always fail, so remove the type inside the not.

The "not" usage around "^x-" patterns for responses is
unnecessary, as the existing

patternProperties:
    "[1-5]..."
additionalProperties: false

prevents all property that do not start with 1, 2, 3, 4, or 5
from being allowed already.