Use libz directly from the NDK.

Now the NDK headers are up to date, we don't need to bundle a copy of
zlib just to access one function (deflateGetDictionary) that's been
available since API level 28. Previously libz_current was the workaround.

Bug: https://issuetracker.google.com/155351357
Test: treehugger
Change-Id: I6b24679de7b5509da985983c3d7c412444891c4d
1 file changed