Remove `infback.c` which we don't need.
The `OF` macro was also removed so I can drop the patch where I yell
at Gentoo developers.
(cherry picked from commits e0e1f2e4a2
and 071499ac0d)
Security update, fixes CVE-2018-25032 in zlib.
Preliminary assessment doesn't show Godot as affected since we don't
seem to call `deflate` with the problematic parameters, but the extent
of the vulnerability is not fully clear upstream yet.
(cherry picked from commit 420d0d50bc)
