dao/bleve: replace Readdir(-1) with os.ReadDir

[Juneezee]

We can simplify the following code

dir, err := os.Open(dirname)
if err != nil {
    return err
}
defer dir.Close()

dirs, err := dir.Readdir(-1)

with just os.ReadDir(dirname)

[cdujeu]

Hey @Juneezee thanks for submitting ! Can you kindly sign the CLA? Otherwise we cannot merge your PR !

[Juneezee]

Hey @Juneezee thanks for submitting ! Can you kindly sign the CLA? Otherwise we cannot merge your PR !

@cdujeu I have signed the CLA, please recheck. Thank you :smiley: