sstable_directory: Move most of .commit_directory_changes() on lister

Committing any changes made while scanning the storage is
storage-specific. Just like .process() was moved on lister, the
.commit() now does the same.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

sstables/sstable_directory.cc

@@ -248,12 +248,13 @@ future<> sstable_directory::components_lister::process(sstable_directory& direct
     }
 }
 
-future<>
-sstable_directory::commit_directory_changes() {
-    auto files_for_removal = std::exchange(_lister->_state->files_for_removal, {});
-    _lister.reset();
+future<> sstable_directory::commit_directory_changes() {
+    return _lister->commit().finally([x = std::move(_lister)] {});
+}
+
+future<> sstable_directory::components_lister::commit() {
     // Remove all files scheduled for removal
-    return parallel_for_each(std::move(files_for_removal), [] (sstring path) {
+    return parallel_for_each(std::exchange(_state->files_for_removal, {}), [] (sstring path) {
         dirlog.info("Removing file {}", path);
         return remove_file(std::move(path));
     });

sstables/sstable_directory.hh

@@ -93,6 +93,7 @@ public:
         future<> close();
 
         future<> process(sstable_directory& directory, fs::path location, process_flags flags);
+        future<> commit();
     };
 
 private: