Further makefile refactorings

* src/bpf_pflua_ts.lua:
* src/bpf_libpcap_ts.lua:
* src/gen_dataset.lua:
* src/bpf_kernel_ts.lua: Remove.

* src/Makefile: Streamline.
Simplify directory structure

* src/linux-ebpf-jit:
* src/linux-bpf-jit:
* src/test-native: Move up a dir level.

* src/ref/linux-tools-net: Remove; unneeded.

* src/bench.lua:
* src/Makefile: Adapt.
Move src/ up a level, and move savefiles up to top level

It seemed silly to have so much structure.