package/putty: bump to version 0.75

Upstream does not set -Werror in its build files anymore.  License file
just changed copyright years and holders.  PGP signatures of source
tarball and hashes were checked.

Link: https://www.chiark.greenend.org.uk/~sgtatham/putty/releases/0.75.html
Link: https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html


Signed-off-by: Alexander Dahl <post@lespocky.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>