busybox: store applet usage messages uncompressed

busybox: store applet usage messages uncompressed

The rootfs squashfs is already highly (XZ) compressed. Storing the applet
messages in compressed form will increase the entropy and reduce the overall
image compression ratio.

Size diffs (compressed vs uncompressed):

busybox (the executable): 364596 vs 384804 bytes.

OpenWrt target images (the kernel image is unchanged, obviously):

 omnia-medkit-openwrt-mvebu-cortexa9-cznic_turris-omnia-initramfs.tar.gz:

  9163597 vs 9162531 bytes (1066 bytes difference).

openwrt-mvebu-cortexa9-cznic_turris-omnia-initramfs-kernel.bin:

  9161688 vs 9160600 bytes (1088 bytes difference).

openwrt-mvebu-cortexa9-cznic_turris-omnia-sysupgrade.img.gz:

 9729550 vs 9729230 bytes (320 bytes difference).

All in all, we save just a little bit over 1 kiB. As an added bonus, we
also don't have to decompress the messages twice, (first from squashfs,
then from the bzip2 message storage).

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
[added additional size comparision diff detaisl]
Signed-off-by: Petr Štetiar <ynezz@true.cz>