Remove generated code from shim-protos (and fix CI)

[mxpv]

While working on #97 I found an interesting issue. Since we currently commit all generated code, we should pin protobuf version to be exactly 3.1.0. Otherwise, whenever Protobuf crate gets updated, shim-protos will be broken with something like:

--> crates/shim-protos/src/cgroups/gogo.rs:26:49
[413](https://github.com/containerd/rust-extensions/actions/runs/3129846807/jobs/5079425017#step:4:414)
   |
[414](https://github.com/containerd/rust-extensions/actions/runs/3129846807/jobs/5079425017#step:4:415)
26 | const _PROTOBUF_VERSION_CHECK: () = ::protobuf::VERSION_3_1_0;
[415](https://github.com/containerd/rust-extensions/actions/runs/3129846807/jobs/5079425017#step:4:416)
   |                                                 ^^^^^^^^^^^^^ help: a constant with a similar name exists: `VERSION_3_2_0`

This is because, according to semver, when we define protobuf = "3.1.0" in Cargo.toml, cargo may use any newer version up to < 2.0.0.

Another approach, more preferable in Rust, is to exclude any generated code from repo, and use include! macro instead. See bindgen example: https://rust-lang.github.io/rust-bindgen/tutorial-4.html

The only thing to keep in mind about include! macro is that it does not support any form of #![allow(XYZ)] attributes, so we have to remote those to build time (and define at crate level) - rust-lang/rfcs#752

Signed-off-by: Maksym Pavlenko pavlenko.maksym@gmail.com

[Burning1020]

LGTM