[LSC] Add LOCAL_LICENSE_KINDS to external/Reactive-Extensions/RxCpp am: 6e6c469a7c

Original change: https://android-review.googlesource.com/c/platform/external/Reactive-Extensions/RxCpp/+/1588615

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ib7a0c0f03465ae73bc82f4fd5f035b538a3a26f7