sw: Remove fetch handler from service worker

In current state, service worker overloads every "connection error"
kind of reaction to a plaintext 200 saying "Offline.", which leads
to terribly undebuggable situations as the browser decides to cache
this as an image, and then someone's pfp is broken literally
forever unless you Ctrl+Shift+R every time you reload frontend.

This change removes the handler, because it is unclear how we even
benefit from it being there.

packages/sw/src/sw.ts

@@ -23,13 +23,6 @@ self.addEventListener('activate', ev => {
 	);
 });
 
-self.addEventListener('fetch', ev => {
-	ev.respondWith(
-		fetch(ev.request)
-		.catch(() => new Response(`Offline. Service Worker @${_VERSION_}`, { status: 200 }))
-	);
-});
-
 self.addEventListener('push', ev => {
 	// クライアント取得
 	ev.waitUntil(self.clients.matchAll({