nrfconnect: Clean up syntax

pkgs/by-name/nr/nrfconnect/package.nix

···
 {
   lib,
+  stdenv,
   fetchurl,
   appimageTools,
+  segger-jlink-headless,
 }:
 
 let
···
   inherit pname version src;
 
   extraPkgs = pkgs: [
-    pkgs.segger-jlink-headless
+    segger-jlink-headless
   ];
 
   extraInstallCommands = ''
···
     install -Dm444 ${appimageContents}/usr/share/icons/hicolor/512x512/apps/nrfconnect.png \
       -t $out/share/icons/hicolor/512x512/apps
     substituteInPlace $out/share/applications/nrfconnect.desktop \
-      --replace 'Exec=AppRun' 'Exec=nrfconnect'
+      --replace-fail 'Exec=AppRun' 'Exec=nrfconnect'
   '';
 
   meta = {