Tab bar settings: fix MIME type filtering of custom CSS file picker
KUrlRequester::filter property does not support MIME type names since KF5, support was lost with switch KFileDialog->QFileDialog for kdelibs4->KF5.
A MIME type filter now needs to be set by the method setMimeTypeFilters.
Separate commits removes ununsed (&broken) css MIME type file filter in Temporary file settings. ab75e68b looks like that was added unnoticed by accident, possibly copied from the other KUrlRequester? :)
Edited by Friedrich W. H. Kossebau