bt2: make `BoolValue` inherit `_IntegralValue`

bt2: make `BoolValue` inherit `_IntegralValue`

This is just like

    issubclass(bool, numbers.Integral)
    issubclass(bool, int)

are true.

It makes `BoolValue` behave even more like `bool`, for example you can
now do:

    3 << bt2.BoolValue(True)

(which is 6).

Also remove BoolValue.__eq__() because _NumericValue.__eq__() does the
job now.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Icbcd8d41b9f064c77586e0b7bfdf4a772c15f0f7
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1565
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>