[FIX] mail: File deletion on module uninstallation
[FIX] mail: File deletion on module uninstallation

PR #30798 introduced thread, message, and attachments deletion on a
module uninstallation. When removing attachments it was also removing
files in the filestore even if those files were still in use by other
attachments.

opw-1968117

closes odoo/odoo#32682

Signed-off-by: Nicolas Martinelli (nim) <771435c469f83f6aa9c405ac5e1ed06314a94f2d@odoo.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo