Revert "amount_generator: getBaseAmountQuantity method can differ per amount generator line."

This reverts commit 6430ccc3.

because it's redundant with the fact that we can already distinguish different Trade Model Line within the returned function by using .getAmountGeneratorLine() on the first parameter.

product/ERP5/bootstrap/erp5_core/MixinTemplateItem/portal_components/mixin.erp5.AmountGeneratorMixin.py

@@ -150,17 +150,16 @@ class BaseAmountDict(Implicit):
     return value
 
   def _getGeneratedAmountQuantity(self, base_amount, variation_category_list):
-    amount_generator_line = self.aq_base._amount_generator_line
     try:
-      method = self._cache[(amount_generator_line, base_amount)]
+      method = self._cache[base_amount]
     except KeyError:
-      method = amount_generator_line._getTypeBasedMethod(
+      method = self.aq_base._amount_generator_line._getTypeBasedMethod(
         'getBaseAmountQuantityMethod')
       if method is not None:
         method = method(base_amount)
       if method is None:
-        method = amount_generator_line.getBaseAmountQuantity
-      self._cache[(amount_generator_line, base_amount)] = method
+        method = self.aq_base._amount_generator_line.getBaseAmountQuantity
+      self._cache[base_amount] = method
     if variation_category_list:
       kw = dict(self._method_kw,
                 variation_category_list=variation_category_list)