sdk!: Remove program feature

[joncinque]

Problem

The program feature has existed since v1.3 so that people can use solana-sdk in on-chain programs.

cargo-build-sbf even had a special case where it would enable the program feature when building solana-sdk, but it was removed in anza-xyz/agave#5870.

This means that our current build-sbf script fails when using v2.3 of the tools.

Summary of changes

Remove the program feature from the sdk, and fix the build-sbf script to exclude the sdk, and then try to build without default features.

Rather than adding more excludes, I also changes the build-sbf script to use cargo hack, which is a bit cleaner.

[joncinque]

Well, this actually shows that it's dangerous to remove the program feature, since older versions of cargo build-sbf will expect to enable it, and fail. This means we'll either need to update the solana-cli version to v2.3 with this PR, or keep the program feature.

What do you think is a better approach?

[LucasSte]

Well, this actually shows that it's dangerous to remove the program feature, since older versions of cargo build-sbf will expect to enable it, and fail. This means we'll either need to update the solana-cli version to v2.3 with this PR, or keep the program feature.

What do you think is a better approach?

Newer versions of cargo-build-sbf will ignore the flag. What about removing solana-sdk from the tests by now (i.e insert it in the exclude list) and keeping the feature flag until we update the CLI version?

Perhaps, it would be worth it to add a comment explaining that the flag is deprecated.

[joncinque]

What about removing solana-sdk from the tests by now (i.e insert it in the exclude list) and keeping the feature flag until we update the CLI version?

That probably makes more sense, since we're essentially saying "don't use solana-sdk on-chain" by removing the "program" feature. Done!