This legacy package was supposed to be an alias to `odoo.upgrade`.
However, depending on how your import its sub-packages (and in which
order), we were ending with the module being loaded multiple times,
breaking the expectation of a singleton.
```python
In [1]: from odoo.addons.base.maintenance.migrations import util as m1
In [2]: import odoo.addons.base.maintenance.migrations.util as m2
In [3]: m1
Out[3]: <module 'odoo.upgrade.util' from '/Users/chs/devel/odoo/odoo/stable/odoo/addons/base/maintenance/migrations/util.py'>
In [4]: m2
Out[4]: <module 'odoo.addons.base.maintenance.migrations.util' from '/Users/chs/devel/odoo/odoo/stable/odoo/addons/base/maintenance/migrations/util.py'>
In [5]: from odoo.addons.base.maintenance.migrations import util as m3
In [6]: m3
Out[6]: <module 'odoo.addons.base.maintenance.migrations.util' from '/Users/chs/devel/odoo/odoo/stable/odoo/addons/base/maintenance/migrations/util.py'>
In [7]: m2 == m3
Out[7]: True
In [8]: m1 == m3
Out[8]: False
In [9]:
```
Now, with this import hook, we ensure that the modules imported from
`odoo.addons.base.maintenance.migrations` are aliases to ones imported
from `odoo.upgrade`.
```python
In [1]: import odoo.addons.base.maintenance.migrations.util as m2
In [2]: m2.__name__
Out[2]: 'odoo.upgrade.util'
```
closesodoo/odoo#71351
X-original-commit: 0d0458a0f370f872caacac26361f2c4730c2cbba
Signed-off-by: Christophe Simonis <chs@odoo.com>
Co-authored-by: Christophe Simonis <chs@odoo.com>