Remove cronet for finalized SDK 31

Cronet was removed from S in b/188872256, but it was not cleaned up
properly. These files suggest cronet is in S, which it isn't.

Bug: 188872256
Test: TH
Change-Id: I0e55963e2d7538ad89dd9b357d6042681c77dc21
Merged-In: I0e55963e2d7538ad89dd9b357d6042681c77dc21
12 files changed