Fixed #23991 -- Apparently, Oracle doesn't need the decimal field converter

Thanks Josh Smeaton for review.

django/db/backends/oracle/base.py

@@ -274,8 +274,6 @@ WHEN (new.%(col_name)s IS NULL)
             converters.append(self.convert_binaryfield_value)
         elif internal_type in ['BooleanField', 'NullBooleanField']:
             converters.append(self.convert_booleanfield_value)
-        elif internal_type == 'DecimalField':
-            converters.append(self.convert_decimalfield_value)
         elif internal_type == 'DateField':
             converters.append(self.convert_datefield_value)
         elif internal_type == 'TimeField':
@@ -311,9 +309,6 @@ WHEN (new.%(col_name)s IS NULL)
             value = bool(value)
         return value
 
-    def convert_decimalfield_value(self, value, field):
-        return backend_utils.typecast_decimal(field.format_number(value))
-
     # cx_Oracle always returns datetime.datetime objects for
     # DATE and TIMESTAMP columns, but Django wants to see a
     # python datetime.date, .time, or .datetime.