$NetBSD$

Use "stb/stb_image.h" file downloaded by pkgsrc.

--- CMakeLists.txt.orig	2022-01-24 15:11:50.000000000 +0000
+++ CMakeLists.txt
@@ -28,10 +28,6 @@ if(ENABLE_ARCUS)
     endif()
 endif()
 
-#For reading image files.
-find_package(Stb REQUIRED)
-include_directories(${Stb_INCLUDE_DIRS})
-
 option(USE_SYSTEM_LIBS "Use the system libraries if available" OFF)
 if(USE_SYSTEM_LIBS)
     find_package(RapidJSON CONFIG REQUIRED)