Import platform SDK from build 7511229

./update_prebuilts.py -f 31 7511229

Manually remove the coreplatform stubs as they are no longer needed.

Bug: 192227286
Test: presubmit
Merged-In: I6f82934cdcf08d4db5b8b639386fded75bdb0e38
Change-Id: Iae4367f479c3c394207d6a6ff45ca2704a901a0e
15 files changed