clatd: remove spurious MTU_DELTA define am: e4aa7b0879 am: 45839c8faa

Original change: https://android-review.googlesource.com/c/platform/external/android-clat/+/2490815

Change-Id: I08bbb73349b73d6eac7412e00a9d62cc0313d696
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>