tests: tls_configurations: remove tests on native/64 platform

Since the same test might be run in parallel on different platforms,
the one that it's started later will fail due to port re-use for
the OpenSSL server.
Since it's not really required to run the tests on native_sim and
native_sim/native/64, the latter is removed in order to solve this
problem.

Signed-off-by: Valerio Setti <vsetti@baylibre.com>