[fix][doc] Remove redundant steps in doc generation

[SignorMercurio]

Matching PR in forked repository

SignorMercurio#3

Motivation

Docs for Pulsar CLI tools such as pulsar-admin, pulsar-client, pulsar and pulsar-perf are auto-generated but contains redundant steps that will produce complex but not useful TOCs(table of content). This PR aims to remove these steps.

Modifications

Remove all ---, Usage and bdocs-tab:example_shell parts since they are no longer useful.

Verifying this change

• [x] Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• [ ] Dependencies (add or upgrade a dependency)
• [ ] The public API
• [ ] The schema
• [ ] The default values of configurations
• [ ] The binary protocol
• [ ] The REST endpoints
• [ ] The admin CLI options
• [ ] Anything that affects deployment

Documentation

• [ ] doc-required (Your PR needs to update docs and you will update later)

• [ ] doc-not-needed (Please explain why)

• [x] doc (Your PR contains doc changes)

• [ ] doc-complete (Docs have been already added)