qemu: fix qemu.ga including qemu in it's closure

The qemu-ga binary is already moved to a separate
output but still depends on qemu, adding about
600MiB to it's closure.

The command "strings qemu-ga" reveals that something
like

/nix/store/bqgpvv5qrpb741swczqk3lrdm5gzaqx2-qemu-host-cpu-only-6.2.0/bin

is contained, causing this false positive. So use
remove-references-to to reduce the closure to about
600KiB.

pkgs/applications/virtualization/qemu/default.nix

@@ -1,7 +1,7 @@
 { lib, stdenv, fetchurl, fetchpatch, python3, python3Packages, zlib, pkg-config, glib, buildPackages
 , perl, pixman, vde2, alsa-lib, texinfo, flex
 , bison, lzo, snappy, libaio, libtasn1, gnutls, nettle, curl, ninja, meson, sigtool
-, makeWrapper, runtimeShell
+, makeWrapper, runtimeShell, removeReferencesTo
 , attr, libcap, libcap_ng, socat
 , CoreServices, Cocoa, Hypervisor, rez, setfile
 , numaSupport ? stdenv.isLinux && !stdenv.isAarch32, numactl
@@ -49,7 +49,7 @@ stdenv.mkDerivation rec {
 
   depsBuildBuild = [ buildPackages.stdenv.cc ];
 
-  nativeBuildInputs = [ makeWrapper pkg-config flex bison meson ninja perl python3 python3Packages.sphinx python3Packages.sphinx_rtd_theme ]
+  nativeBuildInputs = [ makeWrapper removeReferencesTo pkg-config flex bison meson ninja perl python3 python3Packages.sphinx python3Packages.sphinx_rtd_theme ]
     ++ lib.optionals gtkSupport [ wrapGAppsHook ]
     ++ lib.optionals stdenv.isDarwin [ sigtool ];
 
@@ -175,6 +175,7 @@ stdenv.mkDerivation rec {
     # copy qemu-ga (guest agent) to separate output
     mkdir -p $ga/bin
     cp $out/bin/qemu-ga $ga/bin/
+    remove-references-to -t $out $ga/bin/qemu-ga
   '' + lib.optionalString gtkSupport ''
     # wrap GTK Binaries
     for f in $out/bin/qemu-system-*; do