treewide: Lots of meta.hydraPlatforms -> meta.platforms

In all of these files, there is no meta.platforms but only
meta.hydraPlatforms, which doesn't seem to have any purpose except being
inconsistent.

pkgs/development/libraries/libdaemon/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation rec {
 
     license = stdenv.lib.licenses.lgpl2Plus;
 
-    hydraPlatforms = stdenv.lib.platforms.linux;
+    platforms = stdenv.lib.platforms.linux;
     maintainers = [ ];
   };
 }