pebble: .DeleteSync has suspicious nil return for error condition as well as extraneous if err != nil + returns that masked the error

[odeke-em]

If we examine this code, it does an unnecessary if err != nil check that then masks a suspicious nil error that was actually non-nil

If we just did return condition as a simple coding style, there wouldn't be any problems

/cc @elias-orijtech @tac0turtle @julienrbrt

[baabeetaa]

must be copy and paste https://github.com/cometbft/cometbft-db/blob/main/rocksdb.go#L140C13-L140C13

[odeke-em]

I've sent a fix in PR #95