Remove deprecated crc32 and std.md5

This removes two modules that had been deprecated by 6ff6adc5bf7d13b33e27985c53377cd20d7648e6 (Sep 16, 2012).
I was about to remove only crc32, which should be hard to do, but as md5 was deprecated on the same commit, I included it as well. Any breakage introduced by this would be very easy to fix.