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/backup/duply/default.nix

@@ -12,16 +12,15 @@ stdenv.mkDerivation {
 
   buildInputs = [ txt2man makeWrapper ];
 
-  phases = [ "unpackPhase" "installPhase" ];
+  postPatch = "patchShebangs .";
 
   installPhase = ''
     mkdir -p "$out/bin"
     mkdir -p "$out/share/man/man1"
-    sed -i 's|/usr/bin/env bash|${bash}/bin/bash|' duply
-    mv duply "$out/bin"
+    install -vD duply "$out/bin"
     wrapProgram "$out/bin/duply" --set PATH \
-        "${coreutils}/bin:${python}/bin:${duplicity}/bin:${gawk}/bin:${gnupg1}/bin:${bash}/bin:${gnugrep}/bin:${txt2man}/bin:${which}/bin"
-    "$out/bin/duply" txt2man | gzip -c > "$out/share/man/man1/duply.1.gz"
+        ${stdenv.lib.makeBinPath [ coreutils python duplicity gawk gnupg1 bash gnugrep txt2man which ]}
+    "$out/bin/duply" txt2man > "$out/share/man/man1/duply.1"
   '';
 
   meta = with stdenv.lib; {