Removed official/yield.lua since it was only required for lua API 3.x and less (darktable 2.0 and before). Removed require from scripts that had included it.

contrib/hugin.lua

@@ -40,7 +40,6 @@ local du = require "lib/dtutils"
 local df = require "lib/dtutils.file"
 local log = require "lib/dtutils.log"
 local dtsys = require "lib/dtutils.system"
-require "official/yield"
 local gettext = dt.gettext
 
 local namespace = 'module_hugin'
@@ -227,4 +226,4 @@ dt.register_storage(namespace, _("hugin panorama"), show_status, create_panorama
 
 
 --
--- vim: shiftwidth=2 expandtab tabstop=2 cindent syntax=lua
+-- vim: shiftwidth=2 expandtab tabstop=2 cindent syntax=lua