sstrip: remove unneed explicit ccache dependency

This ccache dependency was here to enforce the build order.
It is not needed anymore.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>