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/applications/version-management/git-and-tools/git-radar/default.nix

@@ -4,10 +4,6 @@ stdenv.mkDerivation rec {
   name = "git-radar-${version}";
   version = "0.5";
 
-  phases = [ "unpackPhase" "installPhase" ];
-
-  dontInstallSrc = true;
-
   src = fetchFromGitHub {
     owner = "michaeldfallen";
     repo = "git-radar";
@@ -15,6 +11,8 @@ stdenv.mkDerivation rec {
     sha256 = "1915aqx8bfc4xmvhx2gfxv72p969a6rn436kii9w4yi38hibmqv9";
   };
 
+  dontBuild = true;
+
   installPhase = ''
     mkdir -p $out/bin
     cp git-radar fetch.sh prompt.bash prompt.zsh radar-base.sh $out