Revert "Data model changes"

This reverts commit 089a468a5d.

src/pretix/base/migrations/0142_auto_20191215_1522.py

@@ -1,29 +0,0 @@
-# Generated by Django 2.2.7 on 2019-12-15 15:22
-
-from decimal import Decimal
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('pretixbase', '0141_seat_sorting_rank'),
-    ]
-
-    operations = [
-        migrations.AddField(
-            model_name='cartposition',
-            name='price_before_voucher',
-            field=models.DecimalField(decimal_places=2, max_digits=10, null=True),
-        ),
-        migrations.AddField(
-            model_name='orderposition',
-            name='price_before_voucher',
-            field=models.DecimalField(decimal_places=2, max_digits=10, null=True),
-        ),
-        migrations.AddField(
-            model_name='voucher',
-            name='budget',
-            field=models.DecimalField(decimal_places=2, max_digits=10, null=True),
-        ),
-    ]