This special flag causes the emscripten toolchain to download and build a .zip version of zlib from https://github.com/emscripten-ports/zlib which unnecessarily introduces a network dependency into the build.

We already have a zlib implementation in mono that we can use.

Note that zlib is used both inside of mono and System.Native, we need to make sure only one copy of zlib makes it into the dotnet.wasm.

Three parts to this:

• Remove duplicated zlib files in the build tree
• Use one of the checked-in zlib copies for wasm rather than one downloaded at build time
• Make it possible to link out zlib if System.Compression is unused and runtime is in release (maybe split into separate library? depends on Avoid bundling unnecessary functionality in the wasm published output #48225)