Update to the release version of 0.15, thereby removing the -devel tag
This simplifies things for the port quite a bit since we can now use
Update CONFLICTS to acknowledge removal of rblibtorrent
We need to change the CONFIGURE_ARG to --enable-deprecated-functions
since qbittorrent 2.2.3 uses them.
Remove a no longer needed patch, a better fix was adopted upstream
after my report.