LibJS: Remove GlobalObject from VM::throw_completion()

This is a continuation of the previous five commits.

A first big step into the direction of no longer having to pass a realm
(or currently, a global object) trough layers upon layers of AOs!
Unlike the create() APIs we can safely assume that this is only ever
called when a running execution context and therefore current realm
exists. If not, you can always manually allocate the Error and put it in
a Completion :^)

In the spec, throw exceptions implicitly use the current realm's
intrinsics as well: https://tc39.es/ecma262/#sec-throw-an-exception

Userland/Libraries/LibJS/Runtime/Intl/ListFormat.cpp

@@ -270,7 +270,7 @@ ThrowCompletionOr<Vector<String>> string_list_from_iterable(GlobalObject& global
             // ii. If Type(nextValue) is not String, then
             if (!next_value.is_string()) {
                 // 1. Let error be ThrowCompletion(a newly created TypeError object).
-                auto error = vm.throw_completion<TypeError>(global_object, ErrorType::NotAString, next_value);
+                auto error = vm.throw_completion<TypeError>(ErrorType::NotAString, next_value);
 
                 // 2. Return ? IteratorClose(iteratorRecord, error).
                 return iterator_close(global_object, iterator_record, move(error));