This reverts commit 5d36e382c7919d25e987abf07c40e42e9b2e909e.
It's been found to cause all kinds of terrain glitches on Windows and
Linux. Please do not try experimental image compression alternatives
without discussing and reviewing first.
Overall statistics (only for files with a smaller recompressed size):
Original size: 16720 KiB on 404 files
Optimized size: 15237 KiB
Total saving: 1482 KiB = 8% decrease
