They were there mainly to distinguish from 16-bit Windows, which hasn't
been a thing since before a noticeable fraction of the userbase were
born, probably. These days the obvious comparison is with 64-bit
Windows.
Also tweak some wording to reflect that official PuTTY executables are
not necessarily 32-bit any more, and add some XXX-REVIEW-BEFORE-RELEASE
in the same vein.