Make reuse compliant

src/main/kotlin/moe/nea/firmament/features/FirmamentFeature.kt

@@ -1,19 +1,7 @@
 /*
- * Firmament is a Hypixel Skyblock mod for modern Minecraft versions
- * Copyright (C) 2023 Linnea Gräf
+ * SPDX-FileCopyrightText: 2023 Linnea Gräf <nea@nea.moe>
  *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
 package moe.nea.firmament.features