This commit completely removes the original netx implementation,
which was only used by `tor`, since this has changed in
https://github.com/ooni/probe-cli/pull/652.
The original netx implementation was my first attempt at performing
network measurements using Go. It started its life inside of the
https://github.com/ooni/netx repository. It was later merged into
the https://github.com/ooni/probe-engine repository. It finally
ended up into this repository when we merged probe-engine with it.
The main issue with the original implementation is that it was
a bit too complex and used channels where they were probably not
necessary. Because of that, later I introduced a second netx
implementation, which currently lives in ./internal/engine/netx.
The current netx implementation, the third one, lives in the
./internal/netxlite package. We are currently working to replace
the second implementation with the third one, but this is happening
at a slow pace. Also, the second implementation does not have big
maintenance concerns but it's just a bit too bureaucratic to use
since it involves creating lots of `Config` structures.
The reference issue is probably https://github.com/ooni/probe/issues/1688,
since this diff has been enabled by rewriting Tor to use `measurex`
(a library living on top of `netxlite`).
We are not using them anymore. The only nettest still using the
legacy netx implementation is tor, for which setting these fields
is useless, because it performs each measurement into a separate
goroutine. Hence, let us start removing this part of the legacy
netx codebase, which is hampering progress in other areas.
Occurred to me while doing testing for the recent changes in
error mapping (https://github.com/ooni/probe/issues/1505).
