Remove SkWriter32::contiguousArray().

This method requires SkWriter32 have a contiguous array.
It does, and I plan to keep it that way (last time we checked
it's faster), but this turns that feature back into an
implementation detail.

This feature is only used by another unused feature, deep copies of
ops arrays in SkPictureData.  Kill that, kill this.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1932223003

Depends on https://codereview.chromium.org/1936563002/

Only deleting API
TBR=reed@google.com

Review-Url: https://codereview.chromium.org/1932223003
7 files changed