Remove some unused terminal code

Part of #38414

Author: Tyriar

src/vs/workbench/parts/terminal/common/terminal.ts

@@ -349,16 +349,6 @@ export interface ITerminalInstance {
 	 */
 	setVisible(visible: boolean): void;
 
-	/**
-	 * Attach a listener to the data stream from the terminal's pty process.
-	 *
-	 * @param listener The listener function which takes the processes' data stream (including
-	 * ANSI escape sequences).
-	 *
-	 * @deprecated onLineData will replace this.
-	 */
-	onData(listener: (data: string) => void): IDisposable;
-
 	/**
 	 * Attach a listener to listen for new lines added to this terminal instance.
 	 *

src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts

@@ -823,22 +823,6 @@ export class TerminalInstance implements ITerminalInstance {
 		return env;
 	}
 
-	public onData(listener: (data: string) => void): lifecycle.IDisposable {
-		let callback = (message) => {
-			if (message.type === 'data') {
-				listener(message.content);
-			}
-		};
-		this._process.on('message', callback);
-		return {
-			dispose: () => {
-				if (this._process) {
-					this._process.removeListener('message', callback);
-				}
-			}
-		};
-	}
-
 	public onLineData(listener: (lineData: string) => void): lifecycle.IDisposable {
 		this._onLineDataListeners.push(listener);
 		return {