Eldrune: Asset cleanup (#2135)

This imports the licensing information from #1640, deletes a duplicate
copy of the fireball sound effect, and removes unused template
resources.

Preliminary work for #1707 – I wanted to find the source files for the
music, but this change will not substantially reduce the size of the
game.

Author: wjt

scenes/quests/story_quests/eldrune/0_intro/intro_components/eldrune_intro_image.png

@@ -0,0 +1,14 @@
+version = 1
+
+[[annotations]]
+path = [
+	"crystal stone (1).png",
+	"oldstone (1).png",
+	"stone (1).png",
+	"underwaterstone.png",
+]
+SPDX-FileCopyrightText = [
+	"2018 Melissa Krautheim"
+]
+SPDX-License-Identifier = "CC0-1.0"
+# https://opengameart.org/content/handpainted-stone-texture

scenes/quests/story_quests/eldrune/0_intro/intro_components/eldrune_intro_image.png.import

@@ -0,0 +1,4 @@
+SPDX-FileCopyrightText: Julien_Matthey
+SPDX-License-Identifier: CC0-1.0
+
+https://freesound.org/people/Julien_Matthey/sounds/105016/