[FIX] web: do not set the one2many dirty on field validation

This rev. 06104ba553702b16878d52c5b8ab089355216a5e

Added the dirty flag on the o2m field when the editor of the editable list was enabled (meaning that the editable list has been altered)) because the dirty flag was not set correctly by the one2many during the edition, at the time.

It looks like this is now the case

Besides, as now, we valid all the editable list of the form, wether or not the editable list was altered, we must not set the o2m as dirty anymore.