chromium: remove enableNaCl option

This hasn't worked since 2016 (https://github.com/NixOS/nixpkgs/issues/13983)
and is being removed very soon, per "Q4 2019" in
https://developer.chrome.com/native-client/migration

(It's staying around for "Chrome Apps", but those only run on ChromeOS now.)

earth.google.com users can use https://earth.google.com/web/?beta=1 to get
the wasm version instead of the PNaCl version.

pkgs/applications/networking/browsers/chromium/default.nix

@@ -7,7 +7,6 @@
 
 # package customization
 , channel ? "stable"
-, enableNaCl ? false
 , gnomeSupport ? false, gnome ? null
 , gnomeKeyringSupport ? false
 , proprietaryCodecs ? true
@@ -31,9 +30,7 @@ let
     upstream-info = (callPackage ./update.nix {}).getChannel channel;
 
     mkChromiumDerivation = callPackage ./common.nix {
-      inherit enableNaCl gnomeSupport gnome
-              gnomeKeyringSupport proprietaryCodecs cupsSupport pulseSupport
-              useVaapi;
+      inherit gnome gnomeSupport gnomeKeyringSupport proprietaryCodecs cupsSupport pulseSupport useVaapi;
     };
 
     browser = callPackage ./browser.nix { inherit channel enableWideVine; };