Remove RemoteInputConnectionImpl#mLock, which is redudant am: e47a2e5c06

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/2911222

Change-Id: I33a350506267f7edf6dbaec07f04419c16b9b136
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>