remove writeBitmap from SkWriteBuffer -- unused

Bug: skia:
Change-Id: I8809e7e138d64cc30389e8efc76265011b287611
Reviewed-on: https://skia-review.googlesource.com/77060
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed