compose: Remove old style compose send disable.

We now use `disabled-message-send-controls` class to control
the disabled status of send button. So, this is not required.

web/src/compose_setup.js

@@ -40,7 +40,6 @@ import * as user_topics from "./user_topics.ts";
 import * as widget_modal from "./widget_modal.ts";
 
 export function abort_xhr() {
-    $("#compose-send-button").prop("disabled", false);
     upload.compose_upload_cancel();
 }