Revert "python/aqmp: fix send_fd_scm for python 3.6.x"

This reverts commit 153692ad.

The current code now only requires compatibility with Python 3.8 or later.

The conditional usage of 'sendmsg' on the async IO socket wrapper will generate a deprecation warning on stderr every time send_fd_scm is used with older Python versions.

This has the effect of breaking the QEMU I/O tests when run on Python versions before the 'sendmsg' wrapper was removed.

Unconditionally accessing 'sock._sock' ensures we never use the asyncio socket wrapper, and thus never risk triggering deprecation warnings on any Python version

Signed-off-by: Daniel P. Berrangé berrange@redhat.com