Remove babeltrace 1 Python bindings and tests

We previously had the goal of providing the Babeltrace 1 Python API (the
babeltrace module) on top of the Babeltrace 2 Python API (the bt2
module).

It was decided that this is no longer required, those who have scripts
working against the Babeltrace 1 API will have to keep using Babeltrace
1.

A factor that influenced this decision is that it would be difficult to
keep the exact same behavior as Babeltrace 1 had, and therefore
guarantee that scripts will keep working.  For example, CTF headers
(event headers or packet headers) are not accessible in trace-ir.  So if
a script relied on reading some header fields, the best we could do
would be to simulate the value of some well-known header fields.  For
example, it would be possible to simulate the timestamp field of an
event header.  However, things like a packet's content_size and
packet_size would be more difficult.

So instead of putting efforts doing something that works halfway, it was
decided that such scripts would have to keep using Babeltrace 1.

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>