CMake: pro2cmake: Consider system-assimp for conditions

Change-Id: Idee55dfdd88b04792dc1485a818ab41218fa2707
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

util/cmake/pro2cmake.py

@@ -1569,6 +1569,7 @@ def map_condition(condition: str) -> str:
                     and not feature_name.startswith("system_jpeg")
                     and not feature_name.startswith("system_zlib")
                     and not feature_name.startswith("system_tiff")
+                    and not feature_name.startswith("system_assimp")
                     and not feature_name.startswith("system_doubleconversion")
                 ):
                     part = "ON"