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

This reverts commit 7ed3ceb960.

passbook/providers/saml/migrations/0007_auto_20200303_2157.py

@@ -0,0 +1,29 @@
+# Generated by Django 3.0.3 on 2020-03-03 21:57
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("passbook_crypto", "0001_initial"),
+        ("passbook_providers_saml", "0006_auto_20200217_2031"),
+    ]
+
+    operations = [
+        migrations.RemoveField(model_name="samlprovider", name="signing",),
+        migrations.RemoveField(model_name="samlprovider", name="signing_cert",),
+        migrations.RemoveField(model_name="samlprovider", name="signing_key",),
+        migrations.AddField(
+            model_name="samlprovider",
+            name="singing_kp",
+            field=models.ForeignKey(
+                default=None,
+                help_text="Singing is enabled upon selection of a Key Pair.",
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                to="passbook_crypto.CertificateKeyPair",
+            ),
+        ),
+    ]