`definitions` field can only exist at the top-level

[TomokiMiyauci]

definitions is included in root-schema.
The SharedFormProperties type needs to be improved.

json-typedef-js/src/schema.ts

Lines 112 to 116 in ab4678a

	interface SharedFormProperties {
	definitions?: { [definition: string]: Schema };
	metadata?: { [name: string]: unknown };
	nullable?: boolean;
	}