[Glitch] fix: Prevent scrolling behind menus and modals in Safari iOS

Port c1ef1f62d5 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/utils/scrollbar.ts

@@ -1,19 +0,0 @@
-import { isMobile } from '../is_mobile';
-
-export const getScrollbarWidth = () => {
-  if (isMobile(window.innerWidth)) {
-    return 0;
-  }
-  const outer = document.createElement('div');
-  outer.style.visibility = 'hidden';
-  outer.style.overflow = 'scroll';
-  document.body.appendChild(outer);
-
-  const inner = document.createElement('div');
-  outer.appendChild(inner);
-
-  const scrollbarWidth = outer.offsetWidth - inner.offsetWidth;
-  outer.remove();
-
-  return scrollbarWidth;
-};