Deprecate the Kernel Extension

[russellhancox]

This was originally opened as #663, which resulted in a discussion in #671 and a form for external users to let us know if they wanted us to keep the driver around. The results of that form indicated that the kernel driver is not widely used and is only being utilized on a small number of hosts that have not yet upgraded to newer versions of macOS. As such, continuing to use older versions of Santa that include the driver would be appropriate for those limited use-cases.

As Kent originally stated, removing the kext will allow us to clean up lots of code and make a lot of packaging and distribution tasks much cleaner.