sdcard_image-rpi.bbclass: Remove SDIMG_COMPRESSION
sdcard_image-rpi.bbclass: Remove SDIMG_COMPRESSION

Using SDIMG_COMPRESSION variable to choose compression type for
produced images is deprecated. IMAGE_FSTYPES should be used instead.
This patch removes any response to SDIMG_COMPRESSION within
sdcard_image-rpi.bbclass

Signed-off-by: Iurii Lunev <ac90af2717fd6606c022f7b2aa066377b2ab0b9b@mail.ru>

leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi