Rename algorithm2 to algorithm_prf.

It's purely the PRF function now, although it's still different from the
rest due to the _DEFAULT field being weird.

Change-Id: Iaea7a99cccdc8be4cd60f6c1503df5be2a63c4c5
Reviewed-on: https://boringssl-review.googlesource.com/5614
Reviewed-by: Adam Langley <agl@google.com>
6 files changed