meta/sql: remove lock on edge to avoid deadlock #3677
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When MySQL is used as meta engine, the lock on edge is a gap lock, which can overlap with other directories, can cause deadlock.
Since we always lock the parent directory, so the lock for edge is useless, remove them to avoid deadlock.
Some lock on child node is also removed, since the update of some column is atomic or already protected by the lock of parent dir.
There is still a chance to deadlock in rename, because we have to lock the target sub-directory (for overwrite), which could be locked first by other rename. We left this for database to detect it and retry the transactions.
close #3665