Revert "libvirt: fix dlopen("libjansson.so.4")"

This reverts commit 929a53f281.

Upstream has reverted their move from yajl to jansson after 4.6.0
because of major issues. No point in trying to fix it.
Let's revert to libvirt 4.5.0 and wait for the next upstream release.

pkgs/development/libraries/libvirt/default.nix

@@ -60,9 +60,7 @@ in stdenv.mkDerivation rec {
       --replace 'lxc_path,' '"/run/libvirt/nix-emulators/libvirt_lxc",'
 
     patchShebangs . # fixes /usr/bin/python references
-    substituteInPlace src/util/virjsoncompat.c --replace \
-        '"libjansson.so.4"' '"${jansson}/lib/libjansson${stdenv.targetPlatform.extensions.sharedLibrary}"'
-   '';
+  '';
 
   configureFlags = [
     "--localstatedir=/var"