LADSPA: Update version to 1.15
The 1.13 tarball has been dropped from the project Website, note that the 1.13 tarball has been backed up on GStreamer mirror so that the fallback can work for cerbero builds without this update.
cc @a-morales
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
The 1.13 tarball has been dropped from the project Website, note that the 1.13 tarball has been backed up on GStreamer mirror so that the fallback can work for cerbero builds without this update.
cc @a-morales