[minor issue] initrd.img not cleaned up on kernel update

Hello Igor,

I have noticed for a couple of kernel updates, a very minor issue : the previous initrd.img-x.x.x-sunxi is not removed

I have tested both dpkg -i *.deb or apt upgrade, same issue so I guess a debian pkg script update is needed.

gr@bpi:~$ ls -l /boot
total 13864
drwxr-xr-x 2 root root    4096 Oct 13 15:37 bin
-rw-r--r-- 1 root root    6944 Aug 31 17:48 boot.bmp
-rw-r--r-- 1 root root    1749 Aug 31 17:49 boot.cmd
-rw-r--r-- 1 root root    1821 Aug 31 17:49 boot.scr
-rw-r--r-- 1 root root  115484 Oct 11 14:12 config-4.2.3-sunxi
drwxr-xr-x 2 root root   12288 Oct 13 15:37 dtb
drwxr-xr-x 2 root root    4096 Oct 13 14:23 dtb.old
-rw-r--r-- 1 root root 3294810 Oct 10 23:13 initrd.img-4.2.2-sunxi
-rw-r--r-- 1 root root 3312199 Oct 13 15:38 initrd.img-4.2.3-sunxi
lrwxrwxrwx 1 root root      23 Sep 17 00:46 script.bin -> /boot/bin/lamobo-r1.bin
-rw-r--r-- 1 root root 1955569 Oct 11 14:12 System.map-4.2.3-sunxi
-rwxr-xr-x 1 root root 5468416 Oct 11 14:12 vmlinuz-4.2.3-sunxi
lrwxrwxrwx 1 root root      25 Oct 13 15:38 zImage -> /boot/vmlinuz-4.2.3-sunxi

thanks. Guillaume