fix: don't assign kAgent twice

Author: ronag

lib/dispatcher/proxy-agent.js

@@ -40,7 +40,6 @@ class ProxyAgent extends DispatcherBase {
     const { href, origin, port, protocol, username, password } = url
 
     this[kProxy] = { uri: href, protocol }
-    this[kAgent] = new Agent(opts)
     this[kInterceptors] = opts.interceptors?.ProxyAgent && Array.isArray(opts.interceptors.ProxyAgent)
       ? opts.interceptors.ProxyAgent
       : []