thread/Mutex: remove ScopeLock, use std::lock_guard directly

src/tag/ApeLoader.cxx

@@ -42,7 +42,7 @@ struct ApeFooter {
 bool
 tag_ape_scan(InputStream &is, ApeTagCallback callback)
 try {
-	const ScopeLock protect(is.mutex);
+	const std::lock_guard<Mutex> protect(is.mutex);
 
 	if (!is.KnownSize() || !is.CheapSeeking())
 		return false;

src/tag/Id3Load.cxx

@@ -210,7 +210,7 @@ try {
 UniqueId3Tag
 tag_id3_load(InputStream &is)
 try {
-	const ScopeLock protect(is.mutex);
+	const std::lock_guard<Mutex> protect(is.mutex);
 
 	auto tag = tag_id3_find_from_beginning(is);
 	if (tag == nullptr && is.CheapSeeking()) {