[FIX] account/l10n_ch: QR-Bill - remove border outside of printing zone

In Switzerland, it is mandatory, when a QR bill is printed, to use a line to separate both the QR part from the rest of the page and, within the QR zone, the receipt from the payment part.

This was done using dotted lines on the bill.

However, while generating the PDF caused no problem, the snailmail provider can't print the bottom, far left and far right borders since those are outside of the printing zone.

After further research it does however seem that those are not mandatory, unlike the two separations aforementioned.

Removed those to allow for snailmail printing.

opw-3223714

closes odoo/odoo#119524

Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>