remove unused SkReadBuffer features

No need to keep the list of all those old unsupported version tags.

Everything related to SkDeduper.h was dead code.

fMemoryPtr was just an always null pointer.

SkReadBuffer::clone() doesn't do anything interesting.

DEBUG_NON_DETERMINISTIC_ASSERT doesn't do anything at all.

The whole custom factory feature was unused except by its unit test
and one other, which was using it to avoid a race to register those
types as deserializable.  I think some good old fashioned static
initialization can come to our rescue here...

Change-Id: Ie99dc957fc1035886bb55eaa3fc3339e73f9c320
Reviewed-on: https://skia-review.googlesource.com/c/163984
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
9 files changed