Add on delete cascade to signups user_id column

crates/collab/migrations/20220913211150_create_signups.down.sql

@@ -7,4 +7,3 @@ ALTER TABLE users
 DROP SEQUENCE metrics_id_seq;
 
 DROP INDEX index_users_on_email_address;
-DROP INDEX index_users_on_github_user_id;

crates/collab/migrations/20220913211150_create_signups.up.sql

@@ -7,8 +7,8 @@ CREATE TABLE IF NOT EXISTS "signups" (
     "email_confirmation_sent" BOOLEAN NOT NULL,
     "metrics_id" INTEGER NOT NULL DEFAULT nextval('metrics_id_seq'),
     "created_at" TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    "user_id" INTEGER REFERENCES users (id),
-    "inviting_user_id" INTEGER REFERENCES users (id),
+    "user_id" INTEGER REFERENCES users (id) ON DELETE CASCADE,
+    "inviting_user_id" INTEGER REFERENCES users (id) ON DELETE SET NULL,
 
     "platform_mac" BOOLEAN NOT NULL,
     "platform_linux" BOOLEAN NOT NULL,