fix: DeleteUser in users model

previously, the DeleteUser function was not working as it chained
`.Delete(&user)` after `.First(&user)`. this resulted in a query as
shown, and its corresponding error:

* `ERROR: table name "users" specified more than once (SQLSTATE 42712)
[8.059ms] [rows:1] UPDATE "users" SET "deleted_at"='2024-02-12
20:52:41.02' FROM "users" WHERE id = 4 AND "users"."deleted_at" IS NULL
AND "users"."id" = 4`

the intent of `.First(&user)` was likely to store the user to be deleted
first in the `user` variable with the use of a `SELECT` SQL statement.
however, chaining another method at the end of a finisher method likely
led to some errors (see chaining
[here](https://gorm.io/docs/method_chaining.html)).

thus, this commit attempts to separate the two statements, preserving
the initial intent of storing the user to be deleted before deleting,
and then returning this user.

model/users.go

@@ -54,11 +54,19 @@ func DeleteUser(db *gorm.DB, userID int) (User, error) {
 	err := db.
 		Model(&user).
 		Where("id = ?", userID).
-		First(&user). // store the value to be returned
+		First(&user).
+		Error
+	if err != nil {
+		return user, database.HandleDBError(err, "user")
+	}
+
+	err = db.
+		Model(&user).
 		Delete(&user).
 		Error
 	if err != nil {
 		return user, database.HandleDBError(err, "user")
 	}
+
 	return user, nil
 }