CMake: Remove TODO note in device_key list input source file

The Device Key API is a security API that relies on storage. It is not a storage API

Author: hugueskamba

drivers/device_key/CMakeLists.txt

@@ -1,12 +1,10 @@
 # Copyright (c) 2020 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-# This is a specific driver for the mbed-storage CMake target.
-# TODO CMake: Perhaps move this/these file(s)
 target_include_directories(mbed-device_key
     INTERFACE
-        ./include
-        ./include/device_key
+        include
+        include/device_key
 )
 
 target_sources(mbed-device_key