MDL-74320 lesson: Remove tested elsewhere parts of the scenario
The scenario has not only grades related completion conditions
but also timing conditions or reach the end conditions that
shouldn't be tested by a grades feature.
More yet, those completion conditions are already tested by
other feature files, namely:
- reach the end: completion_condition_end_reached.feature
- visit and timing: lesson_activity_completion.feature
So we have removed all those parts that are being tested
by other features.
Specially the visit and timing ones, because they lead to
random failures in slow environments and they have been
fixed in the lesson_activity_completion.feature scenarios
by MDL-72698.