This PR made merge gracefully remove merged segment by moving
them into `compactedSegments`
And everytime when delete_node operates, if compactedSegments
have contents, delete_node will replace the latest segment in delBuf
merged from the merged segments, and truely remove the compactedSegments
Fixes: #14085
Signed-off-by: yangxuan <xuan.yang@zilliz.com>