Remove broken macOS flags

Due to a typo (a space was missing before the second '-L'), the
resulting LDFLAGS value was broken:

    "-L/opt/homebrew/opt/zlib/lib-L/opt/homebrew/opt/libiconv/lib"

This proves that the flag was useless. Remove it.

Refs #5517 comment <https://github.com/Genymobile/scrcpy/pull/5517#issuecomment-2495522201>
PR #5644 <https://github.com/Genymobile/scrcpy/pull/5644>