Remove explicitly unimplemented importScripts

We have no plans to ever implement `importScripts()` and having
it defined but marked explicitly non-implemented is causing issues
with using certain third-party libraries in workers. So let's just
remove it entirely.

Refs: #1521

src/workerd/api/global-scope.h

@@ -131,15 +131,11 @@ class PromiseRejectionEvent: public Event {
 
 class WorkerGlobalScope: public EventTarget, public jsg::ContextGlobal {
 public:
-  jsg::Unimplemented importScripts(kj::String s) { return {}; };
-
   JSG_RESOURCE_TYPE(WorkerGlobalScope) {
     JSG_INHERIT(EventTarget);
 
     JSG_NESTED_TYPE(EventTarget);
 
-    JSG_METHOD(importScripts);
-
     JSG_TS_DEFINE(type WorkerGlobalScopeEventMap = {
       fetch: FetchEvent;
       scheduled: ScheduledEvent;