Remove migrated methods from HoodieAvroUtils and consolidate remaining functionality.

Scope: org.apache.hudi.avro.HoodieAvroUtils

Changes: Remove methods that were migrated to HoodieSchemaUtils, consolidate remaining Avro-specific utilities, update documentation

Strategy: Method-by-method removal with validation, identify any remaining dependencies on old methods

Constraints: Keep essential record serialization methods, maintain timeline metadata compatibility

Files: HoodieAvroUtils.java, update all remaining callers