Incompatible with projects using protobuf 2.28

[kornelski]

In Cargo dependency versions are deduplicated across the entire workspace (per each major version). The hardcoded dependency protobuf in tensorflow forces all users of tensorflow to use exactly this version of protobuf 2.27.1. It causes a fatal error when resolving dependencies if any dependency anywhere wants protobuf 2.28.

Unfortunately, this version requirement is very public and global. In Cargo the exact = version requirements are quite disruptive. Please don't hardcode the version. If you can't use 2.28, consider forking the crate and depending on the fork, which will not conflict with other uses of the protobuf crate.

https://github.com/tensorflow/rust/blob/62a3019cfa0720c9744b4bd5f97db953bf4066cf/Cargo.toml#L31-L32

[dskkato]

I think the protobuf version limitation is unintended, so you can remove the =. Below is a note of relevant information.

rust-protobuf releases

• 2.27.1 -> Feb 5th, 2022
• 2.28.0 -> Sep 26th, 2022
• 3.2.0 (latest?) -> Sep 26th, 2022

According to the current Readme, rust-protobuf development is scheduled to move to version 3, and version 2 will soon no longer be maintained. Maybe we should migrate too at some point.

https://github.com/stepancheg/rust-protobuf/blob/master/README.md