Remove outdated code in scripts directory

Trying to build the BPF compiler being used I've found the [Fedora Demo VM](https://github.com/iovisor/bcc/tree/master/scripts) and digging deeper I've gotten to find the [command being used there to build the compiler](https://github.com/iovisor/bcc/blob/master/scripts/bpf_demo.ks.erb#L94). Up to now everything looked promising...

I've tried to build myself the compiler with the same command and after diagnosing the build error `llvm-build: error: invalid target to enable: 'CppBackend' (not in project)` on building I've gotten to the root-cause: the [CppBackend got removed from LLVM 2016](https://github.com/llvm-mirror/llvm/commit/257fabb18605265a79397d35dd79a3973760ffaf)!

A couple of the files in the `scripts` directory hasn't been changed in the last 3 years, therefore I assume that some of them wouldn't work nowadays and can be probably removed... At least the creation of the VM I'm sure that wouldn't work.

Start with scripts/bpf_demo.ks.erb and the compiler-build command at line 94, then inspect the other long-unchanged files in scripts used by the Fedora Demo VM. Verify the llvm-build failure caused by the removed CppBackend before deciding what is obsolete. Done means outdated VM or build files are removed without leaving the documented build path inconsistent.

Written by the indexing model from the issue text.