ResizeObserver is now defined in the latest TS version

Removed @ts-ignore

src/annotator/plugin/pdf.js

@@ -172,12 +172,9 @@ export default class PDF extends Delegator {
 
     // nb. In browsers that don't support `ResizeObserver` the banner height
     // will simply be static and not adjust if the window is resized.
-    //
-    // @ts-expect-error - TS is missing `ResizeObserver`
     if (typeof ResizeObserver !== 'undefined') {
       // Update the banner when the window is resized or the Hypothesis
       // sidebar is opened.
-      // @ts-ignore
       new ResizeObserver(updateBannerHeight).observe(this._warningBanner);
     }
     updateBannerHeight();

src/sidebar/util/observe-element-size.js

@@ -12,9 +12,7 @@
  * @return {() => void}
  */
 export default function observeElementSize(element, onSizeChanged) {
-  // @ts-ignore - TS is missing `ResizeObserver` type definition
   if (typeof ResizeObserver !== 'undefined') {
-    // @ts-ignore
     const observer = new ResizeObserver(() =>
       onSizeChanged(element.clientWidth, element.clientHeight)
     );