treewide: use less phases if not necessary

This removes some skipping of e.g. fixupPhase and cleans up occurences
where this led to duplicating code

pkgs/tools/security/jd-gui/default.nix

@@ -29,7 +29,6 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ upx patchelf ];
 
-  phases = "unpackPhase installPhase";
   unpackPhase = "tar xf ${src}";
   installPhase = ''
     mkdir -p $out/bin
@@ -41,6 +40,8 @@ stdenv.mkDerivation rec {
       $out/bin/jd-gui
   '';
 
+  dontStrip = true;
+
   meta = {
     description = "Fast Java Decompiler with powerful GUI";
     homepage    = "http://jd.benow.ca/";