buildroot

infrastructure: remove leftover of old style hooks

Commit ae2be8d (infrastructure: remove support for old style hooks)
forgot to update an uninstall rule.

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Daniel Hobi <daniel.hobi@schmid-telecom.ch>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>