sdcard_image-rpi: Drop unnecessary sync commands
sdcard_image-rpi: Drop unnecessary sync commands

These commands are unnecessary and seem to mask failures to find the rootfs.ext3
file when re-running the do_image_rpi_sdimg stage without re-running the
preceeding do_image_ext3 stage.

Signed-off-by: Paul Barker <ea07171fd37de70b22964565a4c2bfd2bb2b3061@toganlabs.com>

schnitzeltony/meta-raspi-light,schnitzeltony/meta-raspi-light