gd: security bump to version 2.2.5

gd: security bump to version 2.2.5

Fixes the following security issues:

CVE-2017-6362: Double-free in gdImagePngPtr()
CVE-2017-7890: Buffer over-read into uninitialized memory

Drop patches no more needed:

0001-gdlib-config.patch: @LIBICONV@ is nowadays correct AC_SUBST'ed by
configure

0002-gd_bmp-fix-build-with-uClibc.patch: upstream uses ceil() since
https://github.com/libgd/libgd/commit/6913dd3cd2a7c2914ad9622419f9343bfe956135

While we're at it, add a hash for the license file.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>