fix 'timeit' in headless mode

dev/tests/example.lua

@@ -1,6 +1,7 @@
 test.new_world("demo", "2019", "core:default")
+assert(world.is_open())
 assert(world.get_generator() == "core:default")
-coroutine.yield()
+test.sleep(1)
 assert(world.get_total_time() > 0.0)
 print(world.get_total_time())
 test.close_world(true)

res/scripts/stdlib.lua

@@ -15,6 +15,7 @@ if test then
     test.new_world = core.new_world
     test.close_world = core.close_world
     test.reconfig_packs = core.reconfig_packs
+    test.tick = coroutine.yield
 end
 
 ------------------------------------------------

res/scripts/stdmin.lua

@@ -34,11 +34,11 @@ end
 
 
 function timeit(iters, func, ...)
-    local tm = time.uptime()
+    local tm = os.clock()
     for i=1,iters do
         func(...)
     end
-    print("[time mcs]", (time.uptime()-tm) * 1000000)
+    print("[time mcs]", (os.clock()-tm) * 1000000)
 end
 
 ----------------------------------------------

src/logic/scripting/lua/libs/libtime.cpp

@@ -1,5 +1,4 @@
 #include "engine.hpp"
-#include "window/Window.hpp"
 #include "api_lua.hpp"
 
 using namespace scripting;