Except for mingw-w64-qt5-serialbus* which was built after
2fc2ab6cf0
none of these packages have a checksum anymore (as they use VCS sources after
switching to the KDE fork version).
This commit removes the stale checksum files as they are probably confusing.
This was done via:
```
for p in qt5-* ; do source $p/mingw-w64/PKGBUILD ; [[ ${sha256sums[0]} == SKIP ]] && rm -v $p/*/*-sha256.txt ; done
```
* Only packages for additional modules are covered so far
* Only packages for mingw-w64 target are covered so far
* This leads to small adjustments/unifications within the
PKGBUILDs; not tested yet
Martchus