Remove duplicate Object.defineProperty loop in headless Terminal

The constructor defined property getters/setters twice on _publicOptions;
the first block was immediately overwritten by the second. Align with the
browser public Terminal implementation.

Fixes #5935

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

src/headless/public/Terminal.ts

@@ -40,15 +40,6 @@ export class Terminal extends Disposable implements ITerminalApi {
     };
 
     for (const propName in this._core.options) {
-      Object.defineProperty(this._publicOptions, propName, {
-        get: () => {
-          return this._core.options[propName];
-        },
-        set: (value: any) => {
-          this._checkReadonlyOptions(propName);
-          this._core.options[propName] = value;
-        }
-      });
       const desc = {
         get: getter.bind(this, propName),
         set: setter.bind(this, propName)