trytond: Remove required to sequence (issue348001)

[cedric...@b2ck.com]

Reviewers: ,



Please review this at http://codereview.tryton.org/348001/

Affected files:
M trytond/model/modelsql.py
M trytond/modules/account/account.py
M trytond/modules/account/journal.py
M trytond/modules/account/tax.py
M trytond/modules/account_invoice/invoice.py
M trytond/modules/account_invoice/payment_term.py
M trytond/modules/dashboard/dashboard.py
M trytond/modules/party/address.py
M trytond/modules/party/contact_mechanism.py
M trytond/modules/product_price_list/price_list.py
M trytond/modules/project/work.py
M trytond/modules/purchase/purchase.py
M trytond/modules/sale/sale.py
M trytond/modules/sale_opportunity/opportunity.py
M trytond/modules/stock_location_sequence/stock.py
M trytond/modules/stock_product_location/location.py
M trytond/test/mptt.py