Revert "kalua: zram: experimental support for using block-mount/procd"

This reverts commit 3ef6c62e69b2c5e0168268ca26afe4b374f2a380.

swapon/swapoff is provided by package 'block-mount' which will be added as dependency:
https://lists.openwrt.org/pipermail/openwrt-devel/2013-November/022428.html