Use always system date format

Since #6082 (closed), the field date_format is always '%x' because the date_format from user locale is no more set in the screen context.

assigned to @ced

added tryton type::behavior + 1 deleted label

added 1 deleted label and removed 1 deleted label

review43031002 updated at https://codereview.tryton.org/43031002/#ps1

review40971002 updated at https://codereview.tryton.org/40971002/#ps20001

New changeset ed7118685b9e by Cédric Krier in branch 'default':
Use common date_format on search filter and graph
http://hg.tryton.org/sao/rev/ed7118685b9e

added 1 deleted label and removed 1 deleted label

closed

New changeset 3e821d0785a5 by Cédric Krier in branch 'default':
Add common date_format to fallback to rpc context format
http://hg.tryton.org/tryton/rev/3e821d0785a5