[IMP] stock, stock_account: Remove assign owner button

Removes the "Assign Owner" button from picking form view. Now, the stock
move lines owner is set when the picking is validated (if the owner
field is set of course).
The stock move line field owner_id is also hidden for incoming pickings.

Task #1860575

closes odoo/odoo#34986

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>