remove kde414.networkmanagement

It has been unmaintained for years, being replaced by plasma-nm.

pkgs/top-level/all-packages.nix

···
 
           massif-visualizer = callPackage ../development/tools/analysis/massif-visualizer { };
 
-          networkmanagement = builtins.trace "`kde4.networkmanagement' is replaced by `kde4.plasma-nm', please update your configuration" plasma-nm;
-
           partitionManager = callPackage ../tools/misc/partition-manager { };
 
           plasma-nm = callPackage ../tools/networking/plasma-nm { };