Remove region migration rate limiting from Ratis

[CRZbulabula]

Description

• Remove the custom Ratis RPC type, gRPC factory, and log appender introduced in Extend region migration speed limit to transfers and deletion #18118.
• Restore the default Ratis gRPC log appender so region_migration_speed_limit_bytes_per_second no longer affects Ratis snapshot transfers.
• Keep region migration rate limiting for IoTConsensus and IoTConsensusV2 unchanged.

Motivation

The current Ratis hook does not make the migration speed limit effective in practice. Correctly enforcing the limit requires broader integration with the Ratis transfer path, so this PR removes the partial Ratis behavior until that work is implemented properly.

Testing

• mvn spotless:apply -pl iotdb-core/consensus
• mvn test -pl iotdb-core/consensus: all 27 Ratis tests passed. The overall goal reported 13 unrelated IoTConsensus errors because the test machine had only 7.9 GiB free and triggered DiskSpaceInsufficientException.

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This PR has:

• been self-reviewed.

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Key changed/added classes (or packages if there are too many classes) in this PR

• org.apache.iotdb.consensus.ratis.RatisConsensus
• Removed RateLimitedGrpcRpcType, RateLimitedGrpcFactory, and RateLimitedGrpcLogAppender.