Vp1 fix crash path cleaning
This MR fixes a crash when starting VP1, both in 24.0 and main.
The crash is due to a double-deletion in a QStringList when cleaning the input paths used to search for plugins.
Originally, the cleaning routine used the QList::removeAll(string) to remove invalid paths, but that has problems when run within loops. So, I replaced that by a more pragmatic removeAt(idx). That fixes the crash.
We need this fix in 24.0 as well, because that will be run in ACR too.
The MR is not output-changing and no Athena packages depend on VP1; so, the MR is safe to merge into 24.0.