Diable build for tools per default

- closes https://github.com/assimp/assimp/issues/4593

CMakeLists.txt

@@ -90,7 +90,7 @@ OPTION( ASSIMP_BUILD_ZLIB
 )
 OPTION( ASSIMP_BUILD_ASSIMP_TOOLS
   "If the supplementary tools for Assimp are built in addition to the library."
-  ON
+  OFF
 )
 OPTION ( ASSIMP_BUILD_SAMPLES
   "If the official samples are built as well (needs Glut)."