[FIX] web_editor: BS4, do not suggest XS size for buttons
[FIX] web_editor: BS4, do not suggest XS size for buttons

The XS size for buttons was removed in BS4. We lowered the size for
btn-sm though, so those are the replacement.

task-1878245

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo