chore(pusher-web): remove dead onError callback from PusherListener

SubscriptionConfig.onError was never set by any caller after handleError
was removed from Pusher.tsx. Drop the interface field, private field,
call site, and cleanup assignment to avoid misleading future readers.

Author: r0b1n

packages/pluggableWidgets/pusher-web/src/utils/PusherListener.ts

@@ -15,7 +15,6 @@ export interface EventBinding {
 export interface SubscriptionConfig {
     channelName: string;
     eventBindings: EventBinding[];
-    onError?: (error: Error) => void;
 }
 
 export class PusherListener {
@@ -24,7 +23,6 @@ export class PusherListener {
     private currentChannelName: string | null = null;
     private eventHandlersMap: Map<string, () => void> = new Map();
     private globalCallback: ((eventName: string, data: unknown) => void) | null = null;
-    private onError?: (error: Error) => void;
     private destroyed = false;
 
     constructor(private config: PusherConfig) {
@@ -70,7 +68,6 @@ export class PusherListener {
                     return;
                 }
                 console.error("[PusherListener] Subscription error:", error);
-                this.onError?.(new Error(`Subscription error: ${String(error)}`));
             });
         }
 
@@ -79,9 +76,6 @@ export class PusherListener {
         config.eventBindings.forEach(binding => {
             this.eventHandlersMap.set(binding.eventName, binding.onEvent);
         });
-
-        // Store error handler for reference
-        this.onError = config.onError;
     }
 
     /**
@@ -97,7 +91,6 @@ export class PusherListener {
         this.currentChannelName = null;
         this.globalCallback = null;
         this.eventHandlersMap.clear();
-        this.onError = undefined;
     }
 
     /**