[wifi] Remove WiFi.disconnect() from wifi_mode_ to fix AP_STA mode

WiFi.disconnect() sets _wifiHWInitted=false and _mode=WIFI_OFF, which
causes beginAP to run in AP-only mode (_mode=WIFI_AP). In AP-only mode,
subsequent beginNoBlock() calls hit the ESP8266 compatibility hack in
_beginInternal that redirects to beginAP() instead of starting a STA
connection, creating a connect/disconnect loop.

Without WiFi.disconnect(), _wifiHWInitted stays true and beginAP
correctly enters AP_STA mode, allowing STA reconnection attempts to
work properly alongside the fallback AP.

The wifi_sta_connected() helper from the previous commit is sufficient
to prevent false CONNECTED reports by checking WiFi.localIP() instead
of the AP-contaminated WiFi.status().

esphome/components/wifi/wifi_component_pico_w.cpp

@@ -35,11 +35,6 @@ bool WiFiComponent::wifi_mode_(optional<bool> sta, optional<bool> ap) {
   if (sta.has_value()) {
     if (sta.value()) {
       cyw43_wifi_set_up(&cyw43_state, CYW43_ITF_STA, true, CYW43_COUNTRY_WORLDWIDE);
-    } else {
-      // Disconnect STA to clear stale link state (e.g. CYW43_LINK_JOIN from a
-      // timed-out connection). Without this, restart_adapter() leaves the STA
-      // interface joined and wifi_sta_connect_status_() can falsely report CONNECTED.
-      WiFi.disconnect();
     }
   }