Update upb to fix two bugs in the Ruby library.

…rs#536)

As part of the recent protobuf optimization work, we started generating
Unmarshal and Marshal methods on generated messages. These were done to
support the table-driven implementation within the proto package.

We are renaming Marshal as XXX_Marshal and Unmarshal as XXX_Unmarshal
to make it clear that users are not supposed to call these directly.
There are several reasons for the rename:
* The Marshal method assumes that deterministic is the only option we
would ever support for protos, and is not very forward compatible.
* The presence of a deterministic boolean is confusing for users,
where many set it without considering whether it is necessary.
* The Unmarshal method has a slightly different semantic than the previously
documented proto.Unmarshaler interface. The documented Unmarshal specifies
that Reset is called, while the new method does no such thing. The semantic
difference warrants a rename of the method.
* Some users in the Go community depend on these methods not being
generated by default.

Fixes protocolbuffers#530

… providing a minimal Long interface, see protocolbuffers#527, see protocolbuffers#530

Fix memory leak