scxml: Do not modify state in on-entry

Quote from mailing thread with adouma and aschrijvers
"The oneentry/onexit elements should not be
used to change (persistent) state. They are meant to be used to
adjust the context of the state machine according to the state
being entered/exited. Entering/exiting a state is the result of a
event (or explicit) transition, e.g. something 'already happened'.

Also note that state onentry also/always is triggered during the
initialization of the state machine to reflect the current 'state',
e.g. without any event/transition.
...

Changing persistent state should only be done through/within an event
(or eventless) transition (element)."