system: simple deferred reset function

No need for specific delay for each instance, just use a shared one

code/espurna/web.cpp

@@ -242,7 +242,7 @@ void _onReset(AsyncWebServerRequest *request) {
         return;
     }
 
-    deferredReset(100, CustomResetReason::Web);
+    prepareReset(CustomResetReason::Web);
     request->send(200);
 }