[ConfigNode] Revert procedure-based RegionGroup cleanup and fix RegionMaintainer retries

[CRZbulabula]

Description

Cherry-picks #18404 to rc/2.0.11.

• Restores RegionMaintainer ownership of RegionGroup replica cleanup and processes both create and delete tasks.
• Treats idempotent DataNode responses (region already exists or does not exist) as completed work so retry queues can drain safely.
• Removes obsolete procedure-based RegionGroup cleanup state and moves database cleanup to direct SchemaRegion deletion with queued fallback.
• Preserves current release-branch changes while resolving the import conflicts in ProcedureManager and DataNodeInternalRPCServiceImplTest.
• Reuses the existing localized ProcedureMessages constants for the new DeleteDatabaseProcedure logs.

Verification

• mvn spotless:apply -pl iotdb-core/confignode,iotdb-core/datanode
• mvn -q test-compile -DskipTests -pl iotdb-core/confignode,iotdb-core/datanode -am
• mvn -q test-compile -DskipTests -P with-zh-locale -pl iotdb-core/confignode,iotdb-core/datanode -am
• mvn -q surefire:test -pl iotdb-core/datanode -Dtest=DataNodeInternalRPCServiceImplTest
• PartitionManagerRegionMaintainTest could not be executed because the target branch has unrelated ConfigNode Pipe API compilation mismatches; these files are outside this PR.
• Full Reactor mvn test-compile -DskipTests was blocked in distribution while Maven downloaded the ConfigNode snapshot ZIP from repository.apache.org (truncated transfer).