[REM] website: remove multi-website by country

Short summary:
- People can now use the snippets option to show/hide based on country
- We never use / test / maintain this feature, if it still works since
  its introduction 4 years ago that's by luck
- It is probably barely used, we never got a single question or issue
  about it

-----------

When we introduced the multi-website feature, it came with 2 main use
cases:
1. Multi website by domain -> Every website has its own domain and based
   on that we serve the expected website
2. Multi website by geoip -> Multiple website can have the same domain
   and based on GEOIP/country we serve the expected website

We never really supported, highlighted or promoted the geoip case.
We actually never use it ourselves when doing tests, and we don't
consider it when doing specs / improvements.
At most, only a very few people know about it in Odoo.

That GEOIP case is probably not useful at all, as displaying a whole new
website based on lang is not easy since nothing can be shared out of the
box -> Every website has its own COW records.

For instance, one could think of having its main website A and another
website B on which he just added 3 products specific to that website B
country.
But such a case won't even work properly, as any adaption on website A
won't be reflected on website B (design, theme etc).

closes odoo/odoo#99938

Related: odoo/upgrade#3892
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/data/website_data.xml

@@ -549,7 +549,6 @@
         <!-- Default Website -->
         <record id="default_website" model="website">
             <field name="name">My Website</field>
-            <field name="domain"></field>
             <field name="company_id" ref="base.main_company"/>
             <field name="user_id" ref="base.public_user"/>
         </record>