[Refactor] Drop unused get_github_id wrapper orphaned by #932

[Crystora]

Summary

get_github_id in gittensor/utils/github_api_tools.py:321-323 is a 3-line public function with zero production callers. #932 introduced get_github_identity (which returns GitHubIdentityResult(github_id, status) so callers can distinguish transient failures from invalid auth) and migrated every production site. The wrapper has been dead code since #932 merged.

def get_github_id(token: str) -> Optional[str]:
    """Get GitHub numeric user id (as string) using a PAT."""
    return get_github_identity(token).github_id

grep -rn "get_github_id\b" gittensor/ neurons/ returns only the definition itself. The remaining references — the alias on tests/utils/test_github_api_tools.py:31 and test_get_github_id_retry_logic at lines 364-376 — duplicate retry coverage already in the sibling test_get_github_identity_marks_5xx_as_transient / _marks_rate_limit_as_transient / _marks_bad_json_as_transient tests at lines 384-440.

Motivation

Removes one public symbol from gittensor.utils.github_api_tools with no behavior change and drops a duplicated test. The wrapper creates ambiguity in code review — both get_github_id and get_github_identity return the same github_id in the success case, but only get_github_identity exposes the transient/invalid-auth distinction that #932 was designed to enforce.