Revert "Resolve "Mehrfachzuordnung von Studienbereichen ignoriert SEM_TREE_ALLOW_BRANCH_ASSIGN""

This reverts commit ea4b1fe2.

resources/vue/components/tree/StudipTreeNode.vue

@@ -230,9 +230,7 @@ export default {
     },
     computed: {
         isAssignable() {
-            return this.assignable
-                && this.node.attributes.assignable
-                && !this.notAssignableNodes?.includes(this.node.id);
+            return this.assignable && !this.notAssignableNodes?.includes(this.node.id);
         }
     },
     mounted() {