make: Remove generated files on clean target

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Revert "make: Remove generated files on clean target"

This reverts commit b6c7291b3d1f904b20955c3f9829b8cc92801227.

We already have this cleanup stage in "cleaner" target, I managed
to miss it.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>