Drop `test_esplora_connects_to_public_server`

Drop `test_esplora_connects_to_public_server`

`blockstream.info` is currently down, causing our CI to fail. This
shouldn't really be a thing, so we drop the blockstream.info-based
test here.

More generally, I'm not really a fan of having tests which run
(outside of CI) and call out to external servers - a developer
working on LDK shouldn't have to have internet access to run our
test suite and shouldn't be registering their presence with a third
party to run our tests.