Revert "*: providers and sources -> channels, PolicyModel to PolicyBindingModel that uses custom M2M through"

This reverts commit 7ed3ceb960.

passbook/flows/migrations/0003_auto_20200509_1258.py

@@ -0,0 +1,26 @@
+# Generated by Django 3.0.3 on 2020-05-09 12:58
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("passbook_flows", "0002_default_flows"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="flow",
+            name="designation",
+            field=models.CharField(
+                choices=[
+                    ("authentication", "Authentication"),
+                    ("enrollment", "Enrollment"),
+                    ("recovery", "Recovery"),
+                    ("password_change", "Password Change"),
+                ],
+                max_length=100,
+            ),
+        ),
+    ]