Remove zlib from export_target exceptions.
Remove zlib from export_target exceptions.

Note: contrib/optimizations/slide_hash_neon.h is inside zlib. It is
conditionally included which is why it needs to be in the exceptions.

Bug: chromium:1032721
Change-Id: I1da8bb2b12cfe44fca7ce8a423aa33c5e964f05f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2419043
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Jonah Ryan-Davis <682bdb9e7d8ba359ef169b8db374e7a99d394a46@google.com>

ppy/angle,ppy/angle,ppy/angle,ppy/angle