[wp85] Remove yaffs2 image generation
[wp85] Remove yaffs2 image generation

These images are not supported anymore as legato has evolved
towards a read-only squashfs-based partition for /mnt/legato.

Resolves: LE-9896
Related: LXSWIREF-210
Change-Id: Ia1d73bb219f890d26e4f117626424eaa085aa2a9

legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af