freertos-imabe.bbclass: Dropped freertos-image class override

This issue is fixed upstream and we don't need to override the class
in downstream layers
This reverts commit 34449a8c.

Related: https://git.ostc-eu.org/OSTC/OHOS/manifest/-/issues/73


Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>