[lldb] [llvm] [lldb][Process/FreeBSDKernel] Remove libfbsdvmcore support (PR #181283)

[Ed Maste via llvm-commits]

emaste wrote:

Note also that there should be 3 ways we can debug a FreeBSD kernel:
1. Locally opening `/dev/mem` (inherently FreeBSD-only)
2. Opening a FreeBSD kernel core via libkvm (on FreeBSD) or via libfbsdvmcore (on other operating systems)
3. Using the remote GDB protocol (on any operating system)

I think this change will also remove (3) on non-FreeBSD OSes, but should not need to?

CC @bsdjhb

https://github.com/llvm/llvm-project/pull/181283