[REF] stock, stock_account: indices for fast move unlink

Stock moves records can be unlinked in some cases, for example when
confirming a move containing a kit, the original move is unlinked and
replaced by the moves of the components of the kit.

This commit adds two indices to accelerate the unlink of stock move
records. The fields were the indices are added are foreign key on stock
move, and postgres checks the foreign keys of the rows before deleting
them.

closes odoo/odoo#44337

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>