Clean up --experimental_remote_mark_tool_inputs

`--experimental_remote_mark_tool_inputs` is required for remote persistent workers to function correctly:
* https://www.buildbuddy.io/docs/rbe-platforms/#remote-persistent-worker-properties
* https://docs.engflow.com/re/client/remote-persistent-workers.html#client-side-requirements
* https://github.com/buildfarm/buildfarm/blob/127b6c6ad97cc2fc3933aa95646a219c5473598d/src/main/java/build/buildfarm/worker/Executor.java#L488

This flag was first introduced in Bazel 6.0.0, and doesn't describe any reason users should keep it disabled. As-is, this *appears* to be unnecessary boilerplate for remote persistent workers. One of the following should be done:
1. Enable the flag by default, and target a version for removal.
2. Document the tradeoff that justifies why this flag is off by default.

Start by reading the remote persistent worker requirements linked in the issue and the cited buildfarm worker/Executor.java entry point. Determine whether Bazel should enable --experimental_remote_mark_tool_inputs by default or document why it remains disabled; done means one decision is implemented or the tradeoff is documented, including any removal target.

Written by the indexing model from the issue text.