When installing requirements on MS Windows platform with Python 3.8, the
Pillow requirement is defined two times. This leads to a pip crash.

With this commit, the Pillow requirement is only defined once.

Fixes #40080

closes odoo/odoo#40272

X-original-commit: cce9660c
Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>