Fix license header

Author: multiplemonomials

tools/cmake/python_packagecheck.py

@@ -1,8 +1,5 @@
-"""
-mbed SDK
-Copyright (c) 2020 ARM Limited
-SPDX-License-Identifier: Apache-2.0
-"""
+# Copyright (c) 2020 ARM Limited. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
 
 #file which is invoked by the cmake build system to check if all necessary python packages are installed.