Reverts change to force use of 5.10; 5.15 is now available. am: a3441f28a7

Original change: https://android-review.googlesource.com/c/platform/tools/treble/+/2113706

Change-Id: Ib247fe1a152af1d023e80d312a7b895174c6f5cd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>