Switch Plasma's stable branch to 5.21
Also remove the special rules for breeze and plasma-disks. Breeze dropped its Qt4/KDELibs4 parts with 5.19 and plasma-disk doesn't need anything different from the wildcard rule anymore.
Also remove the special rules for breeze and plasma-disks. Breeze dropped its Qt4/KDELibs4 parts with 5.19 and plasma-disk doesn't need anything different from the wildcard rule anymore.