Clean up SSLContext handling in ops-tracing

[dimaqq]

The comment states:

        # Note that ssl.create_default_context() doesn't allow setting the context.protocol in a
        # way that's the same across Python 3.8 and 3.10 onwards. Whip the context up by hand.

Now that Python 3.8 support has been dropped, the code can be simplified.

https://github.com/canonical/operator/blob/e5ee94a7cf052659edcae0ce7a28f73c96d15b40/tracing/ops_tracing/_export.py#L108-L128