treewide: simplify rev/repo arguments in src

+ use fetchFromGithub where possible

pkgs/data/icons/zafiro-icons/default.nix

@@ -7,7 +7,7 @@ stdenv.mkDerivation rec {
   src = fetchFromGitHub {
     owner = "zayronxio";
     repo = pname;
-    rev = "${version}";
+    rev = version;
     sha256 = "05h8qm9izjbp8pnl9jpbw3y9sddhp0zmg94fm1k4d4hhdqnakqhv";
   };
 

pkgs/data/themes/orion/default.nix

@@ -1,11 +1,13 @@
-{ stdenv, fetchgit, gtk-engine-murrine }:
+{ stdenv, fetchFromGitHub, gtk-engine-murrine }:
 
-stdenv.mkDerivation {
-  name = "orion-1.5";
+stdenv.mkDerivation rec {
+  pname = "orion";
+  version = "1.5";
 
-  src = fetchgit {
-    url = "https://github.com/shimmerproject/Orion.git";
-    rev = "refs/tags/v1.5";
+  src = fetchFromGitHub {
+    owner = "shimmerproject";
+    repo = "Orion";
+    rev = "refs/tags/v${version}";
     sha256 = "1116yawv3fspkiq1ykk2wj0gza3l04b5nhldy0bayzjaj0y6fd89";
   };