[dnm/rfc] remove cilium/ebpf dependency

This replaces use of the main cilium/ebpf package (in oc/cgroups) by own code,
while keeping the usage of cilium/ebpf/asm.

As a result, runc binary is about 1MB smaller, which is 7% savings:

[kir@kir-tp1 runc]$ size runc.before runc
   text	   data	    bss	    dec	    hex	filename
6492732	4615697	 229160	11337589	 acff75	runc.before
6018676	4319913	 228392	10566981	 a13d45	runc

[kir@kir-tp1 runc]$ ls -la runc runc.before
-rwxr-xr-x. 1 kir kir 14687496 Apr  2 16:31 runc
-rwxr-xr-x. 1 kir kir 15749568 Apr  2 16:31 runc.before

I am unsure if the added maintenance cost is worth the savings, so this
is more like an experiment and a request for comments.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin