[ld2420] Drop the setup priority override so setup runs after the UART bus

The component declared setup_priority::BUS, the same tier as the UART
bus itself. At a tie the setup order falls back to registration order,
so on ESP-IDF the component could run setup before uart_driver_install
and the failed write marked the UART bus failed for the whole boot.
Delete the override so the component uses the default DATA priority
like ld2410 and ld2450.

esphome/components/ld2420/ld2420.cpp

@@ -184,8 +184,6 @@ static int32_t get_firmware_int(const char *version_string) {
   return result;
 }
 
-float LD2420Component::get_setup_priority() const { return setup_priority::BUS; }
-
 void LD2420Component::dump_config() {
   ESP_LOGCONFIG(TAG,
                 "LD2420:\n"

esphome/components/ld2420/ld2420.h

@@ -105,7 +105,6 @@ class LD2420Component final : public Component, public uart::UARTDevice {
   void apply_config_action();
   void factory_reset_action();
   void revert_config_action();
-  float get_setup_priority() const override;
   int send_cmd_from_array(CmdFrameT cmd_frame);
   void report_gate_data();
   void handle_cmd_error(uint16_t error);