Revert "redmine: Move optional gems to Gemfile.local" (#424140)

This reverts commit 8e690ed6fc02c77488d3cd3d811b5d9ded400b8b.

See https://github.com/NixOS/nixpkgs/issues/421178

At the time of the initial commit the change worked but for currently unknown reasons it broke ~2 weeks after.

pkgs/by-name/re/redmine/Gemfile

@@ -82,6 +82,8 @@ group :test do
   gem 'bundle-audit', require: false
 end
 
+gem "webrick"
+
 local_gemfile = File.join(File.dirname(__FILE__), "Gemfile.local")
 if File.exist?(local_gemfile)
   eval_gemfile local_gemfile

pkgs/by-name/re/redmine/Gemfile.local

@@ -1 +0,0 @@
-gem 'webrick'