We should remove kernel_care "kernels" from katello db

[maccelf]

If new, kernel_care "kernels" are added, are they cleaned-up at any time? I guess this is necessary if

• a kernel care is unloaded
• a brand new kernel is installed and the kernel-care kernel is no longer necessary

Originally posted by @sbernhard in #33 (comment)

In Katello deb packages are not removed, so we should think about how to do it