Update SDK 28 with the final SDK jar and signature files

The prebuilts checked into prebuilts/sdk/28 are not the
final ones and were missing some last minute APIs that were
added, such as ag/Ic6527969793ebe05eb9c5fa8205558ae788ea572.

It was also missing the api removed txt file.

This CL copies the current pi-dev branch contents of
frameworks/base/api/current.txt, system-currenttxt and
removed.txt into the prebuilts, as well as the android.jar
file that is released via the SDK manager (platform 28,
revision 6.)

Fixes: 116589402 Switch signature files over to the v2 format
Exempt-From-Owner-Approval: Large-scale tooling change
Test: make sdk
Change-Id: Icd355cadae18fa16e8c093cce5415c1889fb4a84
Merged-In: I37050f78617d6c90c4500e2acdecaf26fd381a09
4 files changed