Remote settings: remove the fetched column

[bendk]

This simple change is a good way to introduce the sql_support crate and start the migration system.

Made a couple other fixes along the way:

• Don't make the CLI main method async, that causes panics when running the get or sync commands since those will create a second runtime within the async runtime.
• Added remote-settings-data, which is generated by the CLI, to .gitignore
• Fixed sql_support testing bug for schemas with no indexes.

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