[usb_uart] Drop unused is_usb_uart_channel helper

Its only caller was removed when zigbee_proxy switched to observing a
serial_proxy port instead of owning the UART.

esphome/components/usb_uart/__init__.py

@@ -16,7 +16,7 @@ from esphome.const import (
     CONF_DUMMY_RECEIVER,
     CONF_ID,
 )
-from esphome.core import CORE, ID
+from esphome.core import CORE
 from esphome.cpp_types import Component
 from esphome.types import ConfigType
 
@@ -27,21 +27,6 @@ usb_uart_ns = cg.esphome_ns.namespace("usb_uart")
 USBUartComponent = usb_uart_ns.class_("USBUartComponent", Component)
 USBUartChannel = usb_uart_ns.class_("USBUartChannel", UARTComponent)
 
-
-def is_usb_uart_channel(uart_id: ID) -> bool:
-    """Return True if the given ID refers to a channel of a configured usb_uart device.
-
-    Lets UART device components detect that their uart_id points at a USB UART
-    channel (use_id resolution does not narrow the ID's type) so they can enable
-    USB-specific features such as the RX callback.
-    """
-    return any(
-        channel[CONF_ID] == uart_id
-        for device in CORE.config.get("usb_uart") or []
-        for channel in device[CONF_CHANNELS]
-    )
-
-
 UARTParityOptions = usb_uart_ns.enum("UARTParityOptions")
 UART_PARITY_OPTIONS = {
     "NONE": UARTParityOptions.UART_CONFIG_PARITY_NONE,