remove SkIPoint16 from documentation -- it is private

No-Try: true
Docs-Preview: https://skia.org/?cl=149267
Bug: skia:
Change-Id: Idee5487ceecd84c179f898afe3ebc63926608c56
Reviewed-on: https://skia-review.googlesource.com/149267
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>

Author: reed-at-google

site/user/api/METADATA

@@ -9,7 +9,6 @@
     "SkImage_Reference",
     "SkImageInfo_Reference",
     "SkIPoint_Reference",
-    "SkIPoint16_Reference",
     "SkIRect_Reference",
     "SkMatrix_Reference",
     "SkPaint_Reference",