[REM] base: Removed login_key constraint to avoid errors on log

[moylop260]

When we execute -u all to update all modules, Odoo loads the
constraints as it goes through the modules, without taking into account
that the constraints might be removed or updated in a child module.

In this case the base module adds a constraint to make the login
field unique. Later, the website module replaces this constraint by
making unique the combination of login and website_id, to allow
users to register in the different websites.

The first time, and while there are no users registered on multiple
websites, this doesn't raise any issues. After any users registers in
multiple websites, when we try to run -u all again, base will try to
recreate the constraint with its original definition, but it will fail
as there are already multiple users with the same login (but on
different websites).

This patch is removing in the original definition of the constraint,
leaving the work on the website module to create it with the new
definition, and avoid the error when running -u all.

More here:

• SQL constraints trigger warnings after they're redefined odoo/odoo#40740 (comment)

Odoo tried to fixed here:

• [IMP] improve overridden sql constraints support odoo/odoo#30334
  But it is not working

In the OPW task:

• https://www.odoo.com/my/task/2312592
  They replied the following message:

  After internal discussion, we do not plan
  to support SQL constraint override in the near future.
  Supporting all cases (especially relaxing a constraint in
  various inherited modules) can become unnecessarily complex
  for the added value.

Even if you inherit the method _add_sql_constraints this didn't work
Since that Odoo does not have a way to load a module before to base one

This patch is required in DeployV since that a -u all is executed
in staging instance and the error is used to change the state of the build.

It will help to avoid to make a constraint that will not be used.