zlib.recipe: Remove redundant default_library setting
zlib.recipe: Remove redundant default_library setting

We always pass --default-library=both anyway, and setting it twice
causes a warning.

nirbheek/cerbero,GStreamer/cerbero,GStreamer/cerbero,fluendo/cerbero,nirbheek/cerbero,nirbheek/cerbero,atsushieno/cerbero,fluendo/cerbero,GStreamer/cerbero,atsushieno/cerbero,atsushieno/cerbero,fluendo/cerbero,fluendo/cerbero,nirbheek/cerbero,fluendo/cerbero,GStreamer/cerbero,atsushieno/cerbero,atsushieno/cerbero,GStreamer/cerbero