Fix Typo. Remove Optional Parameter

Author: moretalk

src/templates/exportService.hbs

@@ -14,7 +14,7 @@ import { request as __request } from '../core/request';
 import { OpenAPI } from '../core/OpenAPI';
 {{/if}}
 {{/if}}
-type Writeable<T> = { -readonly [P in keyof T]-?: T[P] };
+type Writeable<T> = { -readonly [P in keyof T]: T[P] };
 
 export class {{{name}}}{{{@root.postfix}}} {
     {{#if @root.exportClient}}