[FIX] web_editor: remove useless code breaking the editor scrolling

Since the editor panel is placed on the right, the content was not
possible to scroll when in a iframe, like for mass mailing. This was
because of some strange code introduced with [1]. As the problem the
mentioned commit says fixing is still fixed without that code, I see
no reason to keep this... especially since it may introduce difference
between readonly and editmode content.

[1]: https://github.com/odoo/odoo/commit/f9bf408a827fa86323bc2d1891cb5173b4781e7b



closes odoo/odoo#59902

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>