chore(Vue3): Remove slot check workaround

With our upgrade to @vue/[email protected] in
https://gitlab.com/gitlab-org/gitlab-ui/-/merge_requests/4900, which
includes the fix for vuejs/core#8869
(vuejs/core#10868) we no longer need this
workaround.

Author: markrian

src/utils/is_slot_empty.js

@@ -1,13 +1,8 @@
 import Vue from 'vue';
-import { isVue3 } from './constants';
 
 // Fragment will be available only in Vue.js 3
 const { Fragment, Comment, Text } = Vue;
 
-function callIfNeeded(fnOrResult, args) {
-  return fnOrResult instanceof Function ? fnOrResult(args) : fnOrResult;
-}
-
 export function isVnodeEmpty(vnode) {
   if (!vnode || (Comment && vnode.type === Comment)) {
     return true;
@@ -33,11 +28,7 @@ export function isVnodeEmpty(vnode) {
 }
 
 export function isSlotEmpty(vueInstance, slot, slotArgs) {
-  const slotContent = isVue3
-    ? // we need to check both $slots and $scopedSlots due to https://github.com/vuejs/core/issues/8869
-      // additionally, in @vue/compat $slot might be a function instead of array of vnodes (sigh)
-      callIfNeeded(vueInstance.$slots[slot] || vueInstance.$scopedSlots[slot], slotArgs)
-    : vueInstance.$scopedSlots[slot]?.(slotArgs);
+  const slotContent = vueInstance.$scopedSlots[slot]?.(slotArgs);
 
   // eslint-disable-next-line unicorn/no-array-callback-reference
   return isVnodeEmpty(slotContent);