remove default ALPN value from sphinx.py

[dnet]

e0d70c3 removed the monkey-patched constructor, however, this call site remained with the additional parameter, which was not expected by pyoprf, resulting in a crash for all sphinx command invocations

[stef]

i think this is not necessary due to https://github.com/stef/liboprf/blob/master/python/pyoprf/multiplexer.py#L356 what is necessary to maybe release a new pyoprf release that contains this?