[FIX] lp:1313689

Remove default value to False for account_id since it breaks existing code. It's the responsability of the parser to fill a blank/None account_id in the statement_line values if the default one provided by account_statement_ext does not apply to the expected behavior

account_statement_base_import/statement.py

@@ -240,7 +240,3 @@ class AccountBankStatementLine(Model):
     _columns = {
         'account_id': fields.many2one('account.account', 'Account'),
     }
-
-    _defaults = {
-        'account_id': False,
-    }