[server] Fix race condition in table/partition deletion ordering

[zhang-arvin]

Summary

• Swap the submission order so that metadata deletion (ZK) is submitted to the ioExecutor before remote directory cleanup
• Since the ioExecutor is a single-threaded pool, slow remote filesystem operations can block the faster metadata deletion, causing flaky test timeouts in CoordinatorEventProcessorTest.testCreateAndDropTable

Fixes #1026

Brief change log

• Swapped the call order in completeDeleteTable() so asyncDeleteTableMetadata() is submitted before asyncDeleteRemoteDirectory()
• Applied the same reordering in completeDeletePartition() for consistency

Test Plan

• Existing CoordinatorEventProcessorTest.testCreateAndDropTable
• The fix addresses the race condition at the root cause level