Revert "Add VPX_TUNE_SSIM and VPX_TUNE_PSNR enums"

This reverts commit 1d8d8f562bf382e47071bb38d13b7ded366820af.

Reason for revert: change the api names will break existing code.

Original change's description:
> Add VPX_TUNE_SSIM and VPX_TUNE_PSNR enums
>
> Change-Id: I3df5af2c60b774e6d395062077542c52db868236

TBR=jingning@google.com,builds@webmproject.org,sdeng@google.com

Change-Id: Ic94c19739f595f4544e8b68892ab9d9c1bbccd79
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
10 files changed