mgmt/mcumgr/lib: Deprecate CONFIG_IMG_MGMT_UL_CHUNK_SIZE
mgmt/mcumgr/lib: Deprecate CONFIG_IMG_MGMT_UL_CHUNK_SIZE

The IMG_MGMT_UL_CHUNK_SIZE is no longer used to control size of
intermediate buffer used for application image chunk processing,
instead directly request trasport buffer is used.

Signed-off-by: Dominik Ermel <1a1d45a9cc0c98a37f8d0a0d2dbe3cacc0b2344f@nordicsemi.no>

finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr