v3: remove all Deprecated methods ahead of next major release

[bigbes]

Goal

As part of the v3 cleanup, remove all methods marked as // Deprecated: ... will be removed in the next major version. These have been superseded by the modern request-based API (e.g., SelectRequest{}.Do(conn) instead of conn.Select(...)).

How to Find Them

Run this command in the repo root:

grep -R "Deprecated.*next major version" --include="*.go" -A2 .

Or refer to the full list in this gist.

You’ll see deprecated methods across:

• Connection (in request.go)
• Connector and pool interfaces (connector.go, pool/*.go)
• Future and iterators (future.go, response_it.go)

Checklist

• [ ] Delete all functions/methods with the deprecation comment:

  // Deprecated: the method will be removed in the next major version, ...
  

• [ ] Remove any associated helper functions or test cases that only exist to support these methods.
• [ ] Ensure all internal and example code uses the new request pattern (e.g., NewSelectRequest().Do(conn)).
• [ ] Update the v3 migration guide/changelog to note these removals (if not already done).

Notes

• Don’t remove methods deprecated for other reasons (e.g., “since Tarantool 1.6.2” without the “next major version” note) - focus only on the ones explicitly marked for v3 removal.
• Don’t break the build: run go test ./... after each batch of deletions.