[FIX] l10n_br: wrong & pointless field redefinition

Fields `amount_type` on `account.tax` and `account.tax.template` are
already defined in the `account` module.
Redefining them here (with the same parameters) breaks every other
module that would have used `selection_add=` on those fields.

Actually, it is the case in `account_tax_python`, and thus, all the
localizations/customizations that depend on it were broken by this one.

~ Old API backport of 5d0d80af ~

addons/l10n_br/account.py

@@ -23,11 +23,6 @@ class account_tax_template(osv.osv):
                'amount_mva': fields.float('MVA Percent', required=True, 
                                           digits=0,
                                           help="Um percentual decimal em % entre 0-1."),
-                'amount_type': fields.selection([('group', 'Group of Taxes'),
-                                                 ('fixed', 'Fixed'),
-                                                 ('percent', 'Percentage of Price'),
-                                                 ('division', 'Percentage of Price Tax Included')],
-                                                string="Tax Computation", required=True)
                }
     _defaults = TAX_DEFAULTS
 
@@ -44,10 +39,5 @@ class account_tax(osv.osv):
                'amount_mva': fields.float('MVA Percent', required=True, 
                                           digits=0,
                                           help="Um percentual decimal em % entre 0-1."),
-               'amount_type': fields.selection([('group', 'Group of Taxes'),
-                                                 ('fixed', 'Fixed'),
-                                                 ('percent', 'Percentage of Price'),
-                                                 ('division', 'Percentage of Price Tax Included')],
-                                                string="Tax Computation", required=True)
                }
     _defaults = TAX_DEFAULTS