B7161682765: Remove unused event.onceOn() method

src/event.js

@@ -97,22 +97,6 @@ export default function event(spec, my) {
 		return that;
 	}
 
-	/**
-	 * Like on() except callback will only be fired once
-	 *
-	 * @deprecated use registerOnce() instead
-	 * @param callback {function}
-	 * @returns {eventBinding}
-	 */
-	that.onceOn = function (callback) {
-		// eslint-disable-next-line no-console
-		console.warn(
-			"Sending onceOn() to an event is deprecated. Send registerOnce() instead.",
-		);
-
-		return that.registerOnce(callback);
-	};
-
 	/**
 	 * Like on() except callback will only be fired once
 	 *

test/events.test.js

@@ -290,18 +290,6 @@ describe("deprecated", () => {
 		expect(console.warn).toHaveBeenCalled();
 	});
 
-	it("onceOn() method delegates to registerOnce", () => {
-		// Arrange: an event
-		let anEvent = event();
-		let spy = jasmine.createSpy("registerOnce");
-
-		anEvent.registerOnce = spy;
-		anEvent.onceOn(spy);
-
-		expect(spy).toHaveBeenCalled();
-		expect(console.warn).toHaveBeenCalled();
-	});
-
 	it("on() category method delegates to register", () => {
 		// Arrange: an event
 		let someEvents = eventCategory();