Removed leftover Improvised Song database (#4594)

db/import-tmpl/skill_improvise_db.txt

@@ -1,8 +0,0 @@
-// Improvise Database
-// Database for skills that can be summoned trough Randomize Spell/Improvised Song (Minstrel/Wanderer Skill).
-//
-// Structure of Database:
-// SkillID,Rate
-//
-// - To remove entry by importing, put 0 on 'Rate'
-