Squash a few more warnings

src/screens/sort_playlist.cpp

@@ -194,7 +194,7 @@ void SortPlaylistDialog::sort() const
 		std::iter_swap(a, b);
 		Mpd.Swap(start_pos+a-playlist.begin(), start_pos+b-playlist.begin());
 	};
-	quick_sort = [this, &song_cmp, &quick_sort, &iter_swap](Iterator first, Iterator last) {
+	quick_sort = [&song_cmp, &quick_sort, &iter_swap](Iterator first, Iterator last) {
 		if (last-first > 1)
 		{
 			Iterator pivot = first+Global::RNG()%(last-first);

src/screens/tiny_tag_editor.cpp

@@ -224,7 +224,7 @@ bool TinyTagEditor::getTags()
 	
 	w.highlight(8);
 
-	auto print_key_value = [this](NC::Buffer &buf, const char *key, const auto &value) {
+	auto print_key_value = [](NC::Buffer &buf, const char *key, const auto &value) {
 		buf << NC::Format::Bold
 		    << Config.color1
 		    << key

src/settings.cpp

@@ -251,7 +251,7 @@ bool Configuration::read(const std::vector<std::string> &config_paths, bool igno
 					+ "\" to preserve current behavior");
 			};
 		});
-	p.add<void>("active_column_color", nullptr, "", [this](std::string v) {
+	p.add<void>("active_column_color", nullptr, "", [](std::string v) {
 			if (!v.empty())
 			{
 				deprecated(