kernel-install plugin fails with uki layout when removing

[SteelT1]

If the install layout is set to "uki", then when removing a kernel image, it doesn't get removed from the signing database by 91-sbctl.install. Causing the entries for previous kernel versions to stick around.

[ksimuk]

Looks like #294 broke the functionality, as the file already removed before 91-sbctl.install by 90-uki-copy.install. Removing from the database doesn't require physical file, and should check if record exist in database

Additionally, if mkinitcpio is used 8e0e68b will register and not remove kernels located in /usr/lib/modules/<version>/vmlinuz