Remove external/ukey2/.gitmodules and submodule directories. am: e711039fa9 am: 492edd667d am: fbfc8c2de3

Original change: https://android-review.googlesource.com/c/platform/external/ukey2/+/1830387

Change-Id: I39b782244d2516ef02aad5f9b23f49337033886b