[efi] Do not try to fetch loaded image device path protocol

Some UEFI systems (observed with a Mac Pro) do not provide a loaded
image device path protocol.  We don't currently use the loaded image
device path protocol for anything beyond printing a debug message, so
simply remove the code which attempts to fetch it.

Reported-by: Matt Woodward <pxematt@woodwardcc.com>
Tested-by: Matt Woodward <pxematt@woodwardcc.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/interface/efi/efi_init.c

 /** Loaded image protocol for this image */
 EFI_LOADED_IMAGE_PROTOCOL *efi_loaded_image;
 
-/** Loaded image protocol device path for this image */
-EFI_DEVICE_PATH_PROTOCOL *efi_loaded_image_path;
-
 /** System table passed to entry point */
 EFI_SYSTEM_TABLE *efi_systab;
 
 static EFI_GUID efi_loaded_image_protocol_guid
 	= EFI_LOADED_IMAGE_PROTOCOL_GUID;
 
-/** EFI loaded image device path protocol GUID */
-static EFI_GUID efi_loaded_image_device_path_protocol_guid
-	= EFI_LOADED_IMAGE_DEVICE_PATH_PROTOCOL_GUID;
-
 /** Event used to signal shutdown */
 static EFI_EVENT efi_shutdown_event;
 
 	struct efi_protocol *prot;
 	struct efi_config_table *tab;
 	void *loaded_image;
-	void *loaded_image_path;
 	EFI_STATUS efirc;
 	int rc;
 
 	DBGC ( systab, "EFI image base address %p\n",
 	       efi_loaded_image->ImageBase );
 
-	/* Get loaded image device path protocol */
-	if ( ( efirc = bs->OpenProtocol ( image_handle,
-				&efi_loaded_image_device_path_protocol_guid,
-				&loaded_image_path, image_handle, NULL,
-				EFI_OPEN_PROTOCOL_GET_PROTOCOL ) ) != 0 ) {
-		rc = -EEFI ( efirc );
-		DBGC ( systab, "EFI could not get loaded image device path "
-		       "protocol: %s", strerror ( rc ) );
-		return efirc;
-	}
-	efi_loaded_image_path = loaded_image_path;
-	DBGC ( systab, "EFI image device path " );
-	DBGC_EFI_DEVPATH ( systab, efi_loaded_image_path );
-	DBGC ( systab, "\n" );
-
 	/* EFI is perfectly capable of gracefully shutting down any
 	 * loaded devices if it decides to fall back to a legacy boot.
 	 * For no particularly comprehensible reason, it doesn't