fix: deprecated_image_key 컬럼 삭제

Author: lvalentine6

src/main/resources/db/migration/V9__drop_cheer_story_deprecated_image.sql

@@ -0,0 +1,4 @@
+ALTER TABLE cheer
+    DROP COLUMN _deprecated_image_key;
+ALTER TABLE story
+    DROP COLUMN _deprecated_image_key;