examples: drop rustfmt example

[daviddrysdale]

This example doesn't show anything that's not demonstrated by other
examples, and it needs nightly channel Rust which keeps causing
problems (and prevents us moving to the stable channel).

Fixes #1075. Fixes #594.

Checklist

• Pull request affects core Oak functionality (e.g. runtime, SDK, ABI)
  • I have written tests that cover the code changes.
  • I have checked that these tests are run by Cloudbuild
  • I have updated documentation accordingly.
  • I have raised an issue to
    cover any TODOs and/or unfinished work.
• Pull request includes prototype/experimental work that is under
  construction.

[rbehjati]

LGTM. Thanks.

[github-actions]

Reproducibility Index:

888dde607bfb080fbb19acb2d757c5a7a8dd14c279bc98eb68c152888a253ff5  ./examples/target/wasm32-unknown-unknown/release/abitest_0_frontend.wasm
aa5df52684fc21571484dcbc9a50955fe26c82a1d05e2b15d2913ac6c540025d  ./examples/target/wasm32-unknown-unknown/release/abitest_1_backend.wasm
8bc7b1323463c608b9dc9bac8bd62bbb5a0c6baa320df1c7c581cd127da90489  ./examples/target/wasm32-unknown-unknown/release/aggregator.wasm
2ddf099c23875f7dce73e41c19dfc2aa9fe3572a795e4e6b96b0356a98853aa5  ./examples/target/wasm32-unknown-unknown/release/chat.wasm
02f986b5334c5d1dae0902387a06a91caa04ee4ba988ab6d1843f75debec0d36  ./examples/target/wasm32-unknown-unknown/release/hello_world.wasm
53414a50383558bce1617b1b752961d75ce3b744664c2c48a7cd79fd856c8ee2  ./examples/target/wasm32-unknown-unknown/release/machine_learning.wasm
19ab3ad7f0b15c7871461a31d73d3e7568315f1d50d59d0a2b37c87d3ffd03dc  ./examples/target/wasm32-unknown-unknown/release/private_set_intersection.wasm
07d7ce6b796738666d35e961a4dd4ee92c79f61b77f8c7c797ca7b9e35868f66  ./examples/target/wasm32-unknown-unknown/release/running_average.wasm
ca42ef3a20ec556bdc5e791971233d7801914b4d03fe7738c5155af7f84e5faa  ./examples/target/wasm32-unknown-unknown/release/translator.wasm
72c19cbd903d963ee1b3f9dda23e4e1528ee2dff304fae03ef51b0ba80fa62f7  ./examples/target/wasm32-unknown-unknown/release/trusted_information_retrieval.wasm
bb1c2f869a9095976073598a86e3da8d322d92a1b35faf0063f69009b4942dd3  ./target/x86_64-unknown-linux-musl/release/oak_loader

Reproducibility Index diff: