zilencer: Remove index on RemoteInstallationCount.remote_id.

As in 902498ec4f, we shouldn't need an
index on remote_id alone - only (server_id, remote_id) together.

zilencer/migrations/0030_alter_remoteinstallationcount_remote_id.py

@@ -0,0 +1,17 @@
+# Generated by Django 4.2.6 on 2023-10-20 00:10
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zilencer", "0029_update_remoterealm_indexes"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="remoteinstallationcount",
+            name="remote_id",
+            field=models.IntegerField(),
+        ),
+    ]