HYBIM-801 Removing GalileoScorers

[shuningc]

Remove GalileoScorers from splunk-ao SDK

Summary

• Removes GalileoScorers deprecated proxy class (_SplunkAOScorersProxyMeta, _SplunkAOScorersProxy)
  from schema/metrics.py
• Removes GalileoScorers re-export from init.py and all
• Deletes tests/test_deprecations.py (all tests covered the now-removed deprecation shim)
• Cleans up unused imports (warnings, Iterator, ScorerName) that were only needed by the proxy

Context

GalileoScorers was previously deprecated in favour of SplunkAOMetrics. Since it is no longer used
anywhere in the SDK, the deprecation shim can be fully removed. Users should use SplunkAOMetrics
instead. See galileo-python#439 for the upstream reference.

Test plan

• All 1904 existing tests pass with no new failures