Remove the normalized config export (#4227)

Closes graphql/graphql-js#3853

There's only one normalizedConfig we export and these are just the type
config with a few extras. I would rather than exporting all of them just
stop exporting them for the time being as we don't accept them as inputs
and it can still be derived by doing
`ReturnType<GraphQLInterfaceType['toConfig']>` if it's really needed

src/type/definition.ts

@@ -1188,7 +1188,7 @@ export interface GraphQLInterfaceTypeConfig<TSource, TContext> {
   extensionASTNodes?: Maybe<ReadonlyArray<InterfaceTypeExtensionNode>>;
 }
 
-export interface GraphQLInterfaceTypeNormalizedConfig<TSource, TContext>
+interface GraphQLInterfaceTypeNormalizedConfig<TSource, TContext>
   extends GraphQLInterfaceTypeConfig<any, any> {
   interfaces: ReadonlyArray<GraphQLInterfaceType>;
   fields: GraphQLFieldConfigMap<TSource, TContext>;