Revert "simplify SkTFitsIn"

This reverts commit b82c3d6ff2ac62c8a14b38b0d658a51e7d8cf81e.

Reason for revert: SkTFitsIn makes its way into public headers via SkTo<T>, so it cannot use C++14isms.

Original change's description:
> simplify SkTFitsIn
> 
> Now that we're C++14, a constexpr SkTFitsIn() is a lot easier.
> All the old tests still pass, and one new added.
> 
> Updated the comments a bit for correctness and readability.
> 
> Change-Id: I0f60e32e545fe4f2fb14e66a2bf25d562dbd680f
> Reviewed-on: https://skia-review.googlesource.com/133831
> Reviewed-by: Ben Wagner <bungeman@google.com>
> Commit-Queue: Mike Klein <mtklein@chromium.org>

TBR=mtklein@chromium.org,halcanary@google.com,bungeman@google.com

Change-Id: Icfb19c77b450cf3525d11225d4237f9bfa68c7fc
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/134440
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed