[FIX] account: add index

Before this commit the time to unlink an account.move can take lot of time (60s on large database).

closes odoo/odoo#161172

X-original-commit: 73c1fdd192577bba56dcad213d8a22de8b5de06f
Signed-off-by: Olivier Colson (oco) <oco@odoo.com>

addons/account/models/account_partial_reconcile.py

@@ -18,7 +18,7 @@ class AccountPartialReconcile(models.Model):
         index=True, required=True)
     full_reconcile_id = fields.Many2one(
         comodel_name='account.full.reconcile',
-        string="Full Reconcile", copy=False)
+        string="Full Reconcile", copy=False, index='btree_not_null')
     exchange_move_id = fields.Many2one(comodel_name='account.move', index='btree_not_null')
 
     # ==== Currency fields ====