alfred,batctl: don't override PKG_CONFIG

was added in 2016 but not necessary anymore

to fix cross compilation

pkgs/os-specific/linux/batman-adv/alfred.nix

···
   buildInputs = [ gpsd libcap libnl ];
 
   preBuild = ''
-    makeFlags="PREFIX=$out PKG_CONFIG=${pkg-config}/bin/${pkg-config.targetPrefix}pkg-config"
+    makeFlags="PREFIX=$out"
   '';
 
   meta = {

pkgs/os-specific/linux/batman-adv/batctl.nix

···
   buildInputs = [ libnl ];
 
   preBuild = ''
-    makeFlags="PREFIX=$out PKG_CONFIG=${pkg-config}/bin/${pkg-config.targetPrefix}pkg-config"
+    makeFlags="PREFIX=$out"
   '';
 
   meta = {