ANDROID: Delete Android.mk to avoid conflicts with other imports. am: c5427947e7 am: ff579d2ec5 am: 95839a5b03 am: 721d6506da

Original change: https://android-review.googlesource.com/c/platform/external/libwebm/+/1504155

Change-Id: Ia7e4b310db6e99bed427cbd810a18991096bc4c3