bt2: _ArrayField.__setitem__(): do not check type

bt2: _ArrayField.__setitem__(): do not check type

There's no need to check the type of the parameter because

    field.value = value

will raise a type error if `value` has an unexpected type.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I0ae91873024e9a52a00bb1ac6f03ff830a19dea7
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1570
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>