lisa.trace: Deprecate Trace.add_event_deltas()
lisa.trace: Deprecate Trace.add_event_deltas()

Adding delta on the event dataframe is not a good idea, as it only makes sense
on events that contain one signal only. Such events are actually extremely rare
since they represent a system-wide property like sched_overutilized.

Instead, using lisa.datautils.df_add_delta() after extracting the signals will
give the correct results.

ARM-software/lisa,ARM-software/lisa,credp/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa,ARM-software/lisa