I'm unsure whether we're planning to make the `Deno.FsFile` constructor
illegal or remove `FsFile` from the `Deno.*` namspace in Deno 2. Either
way, this PR works towards the former. I'll create a superceding PR if
the latter is planned instead.
Towards #23089
This change removes deprecated methods from the `Deno.*` namespace when
the `DENO_FUTURE=1` environment variable is used.
Note: this does not address deprecated class properties and methods.
E.g. `Deno.Conn.rid`.
