cronet: delete cronet prebuilts

Cronet is now built from source, so this code is not used anymore.

Merged-In line is from an unrelated change to prevent this from being
merged into git_master. A separate change will be merged in aosp-master
and will then automerge into git_master.

Test: TH
Merged-In: I8e2a4b76c09c7f11c01f125bf7f48d04aa897393
Change-Id: I2a5ba4d5805fbb56945de74eb14ae9ef510e6f45
30 files changed