Remove unused dylib_ext variable from build.sh

Author: bjorn3

build.sh

@@ -34,7 +34,6 @@ if [[ "$unamestr" == 'Linux' || "$unamestr" == "FreeBSD" ]]; then
    export RUSTFLAGS='-Clink-arg=-Wl,-rpath=$ORIGIN/../lib '$RUSTFLAGS
 elif [[ "$unamestr" == 'Darwin' ]]; then
    export RUSTFLAGS='-Csplit-debuginfo=unpacked -Clink-arg=-Wl,-rpath,@loader_path/../lib -Zosx-rpath-install-name '$RUSTFLAGS
-   dylib_ext='dylib'
 else
    echo "Unsupported os $unamestr"
    exit 1