update.py: handle if deleted recipe can't be found
update.py: handle if deleted recipe can't be found

Show a warning instead of a traceback if a deleted recipe can't be found
in the database.

Signed-off-by: Paul Eggleton <737d4dae46a541673d7bf4e0d5b32714b16528d8@linux.intel.com>

bartosh/layerindex-web,bartosh/layerindex-web,bartosh/layerindex-web