AmendmentDisclaimer: remove vestigial isVoting attribute

Co-authored-by: tequ <git@tequ.dev>

@theme/markdoc/schema.ts

@@ -229,11 +229,6 @@ export const amendmentDisclaimer: Schema &  { tagName: string } = {
       type: 'String',
       required: true
     },
-    isVoting: {
-      type: 'Boolean',
-      required: false,
-      default: false
-    }
   },
   render: 'AmendmentDisclaimer',
   selfClosing: true