Revert "patch sbcl-bootstrap for purity"

This reverts commit 06eab94f1603620944dfcc6c64b5af8c194db75f.
It doesn't even evaluate on Linux and the author doesn't react.

pkgs/development/compilers/sbcl/bootstrap.nix

···
   installPhase = ''
     mkdir -p $out/bin
     cp -p src/runtime/sbcl $out/bin
-    install_name_tool -change /usr/lib/libgcc_s.1.dylib ${stdenv.libc}/lib/libgcc_s.10.5.dylib $out/bin/sbcl
 
     mkdir -p $out/share/sbcl
     cp -p src/runtime/sbcl $out/share/sbcl