whatsapp: remove AllEndpoints option

[bassosimone]

This option increases the false positive rate. If an endpoint is blocked/down and we choose it, then we say that WhatsApp is down when instead it may just be a minor disruption. The Go implementation and the spec have been updated to not mention this option anymore. Using this option on mobile will now trigger a warning.

See ooni/probe-engine#743 (comment)

[lorenzoPrimi]

@bassosimone should I also switch to the Go implementation of whatsapp test?

[bassosimone]

@lorenzoPrimi I think it's fine to start removing the option. If you switch to Go now it breaks b/c you don't have the new engine version that also implements WhatsApp.