db/simple: remove unused method LookupDirectory()

src/db/plugins/SimpleDatabasePlugin.cxx

@@ -235,17 +235,6 @@ SimpleDatabase::ReturnSong(gcc_unused const LightSong *song) const
 #endif
 }
 
-gcc_pure
-const Directory *
-SimpleDatabase::LookupDirectory(const char *uri) const
-{
-	assert(root != nullptr);
-	assert(uri != nullptr);
-
-	ScopeDatabaseLock protect;
-	return root->LookupDirectory(uri);
-}
-
 bool
 SimpleDatabase::Visit(const DatabaseSelection &selection,
 		      VisitDirectory visit_directory,

src/db/plugins/SimpleDatabasePlugin.hxx

@@ -107,9 +107,6 @@ private:
 	bool Check(Error &error) const;
 
 	bool Load(Error &error);
-
-	gcc_pure
-	const Directory *LookupDirectory(const char *uri) const;
 };
 
 extern const DatabasePlugin simple_db_plugin;