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/LibWeb/Fetch/Headers.cpp

@@ -165,7 +165,7 @@ JS::ThrowCompletionOr<void> Headers::for_each(ForEachCallback callback)
     auto value_pairs_to_iterate_over = [&]() -> JS::ThrowCompletionOr<Vector<Fetch::Infrastructure::Header>> {
         auto headers_or_error = m_header_list.sort_and_combine();
         if (headers_or_error.is_error())
-            return vm.throw_completion<JS::InternalError>(global_object, JS::ErrorType::NotEnoughMemoryToAllocate);
+            return vm.throw_completion<JS::InternalError>(JS::ErrorType::NotEnoughMemoryToAllocate);
         return headers_or_error.release_value();
     };