Revert "x2goclient: move to qmake4Hook"

This reverts commit 83406bc171ca2b385c49838e6ed5e89007a875b5, because
it broke the build.

x2goclient requires to be built with its top-level (hand coded) Makefile
(in accordance with upstream documentation). Invoking qmake directly on
the .pro file, without specifying a separate build tree, will overwrite
the Makefile and break the build.

For instance, there are no install rules in the .pro file. That exists
only in the Makefile.

pkgs/applications/networking/remote/x2goclient/default.nix

···
-{ stdenv, fetchurl, cups, libssh, libXpm, nxproxy, openldap, makeWrapper, qt4, qmake4Hook }:
+{ stdenv, fetchurl, cups, libssh, libXpm, nxproxy, openldap, makeWrapper, qt4 }:
 
 stdenv.mkDerivation rec {
   name = "x2goclient-${version}";
···
   };
 
   buildInputs = [ cups libssh libXpm nxproxy openldap qt4 ];
-  nativeBuildInputs = [ makeWrapper qmake4Hook ];
+  nativeBuildInputs = [ makeWrapper ];
 
   patchPhase = ''
      substituteInPlace Makefile \
···
        --replace "-o root -g root" ""
   '';
 
-  preConfigure = ''
-    qmakeFlags="$qmakeFlags ETCDIR=$out/etc"
-  '';
+  makeFlags = [ "PREFIX=$(out)" "ETCDIR=$(out)/etc" ];
 
   enableParallelBuilding = true;