Tests: Removed unused LABELS on CMake's own tests
In commit 44ad3f0b7f (ctest: Support multiple -L and -LE options to mean
"AND", 2021-03-20, v3.21.0-rc1~424^2) we added several labels to CMake's
own tests, perhaps as a way to demonstrate the change made by the
commit. However, they have not been maintained or added to other tests
they cover. Since commit 49e9f817de (ctest: Display test labels in
failure summary, 2024-06-14) the labels are displayed next to failed
test names, making them more visible. Remove these unnecessary labels.