Update prebuilts from build server

CtsShim.apk
versionCode='24' versionName='7.0-2996264'

CtsShimPriv.apk
versionCode='24' versionName='7.0-2996264'

Built here:
https://android-build.googleplex.com/builds/submitted/2996264/CtsShim/latest

This build is suitable for public release.

Bug: 29122339
Change-Id: I6533e3a3ed72de6d3887039e3e8cf527947c4166