[FIX] website: remove data-editor-message attributes on save
[FIX] website: remove data-editor-message attributes on save

When the edit mode is entered, some elements receive
data-editor-message attributes. These were not removed on save which
could in some cases make the attributes be saved in the database. For
this to happen it would require an `.oe_structure.oe_empty` element to
be put *inside* an editable element (instead of being the one which is
editable). In that case the `.oe_structure` content would be saved in an
inheriting view but the parent view would also be COW'd for no reason
because of that attribute.

Difficult to say if such a case exist in the current views but as it
technically possible and that some of our tests use that configuration,
it is worth fixing.
Note: this fix was in fact done in the new editor in master and allowed
to detect that one of our test was not testing a feature correctly
because of that. This will be adapted in a different commit of this PR.

closes odoo/odoo#30834
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo