Update lilv to enable audacity 2.4.2 to build see boo#1179449

- Add specific version requirement for libserd see boo#1158728

- Update to release 0.24.6 fixes boo#1158296
- Upstream changes:
*Add more strict error detection when storing plugin state
properties
*Add option to override LV2_PATH in applications
*Don't print errors when saving state if correct links already
exist
*Fix GCC8 warnings
*Fix creating directories across drives on Windows
*Fix issues with loading state with saved files from the model
*Fix memory errors and Python 3.4+ compatibility in Python bindings
*Fix unit tests on Windows
*Make Python bindings more Pythonic

- Version update to 0.24.4:
* Fix saving state when broken links are encountered
* Don't attempt to load remote or non-Turtle files
* lv2apply: Activate plugin before running
* lv2apply: Use default values when they are not nan
* lv2bench: Improve support for plugins with sequence ports
* lv2bench: Support running a single plugin given on the command line
* Gracefully handle plugins with missing binary URIs
* Remove use of deprecated readdir_r
* Install Python bindings when configured without tests
(thanks Clement Skau)