remove WithMinimumBuffer for MemFile (#820)

internal/bsr/internal/fstest/fs.go

@@ -293,7 +293,6 @@ func NewMemFile(n string, mode sfs.FileMode, options ...Option) *MemFile {
 		statFunc:      opts.withStatFunc,
 		closeFunc:     opts.withCloseFunc,
 		bufferSize:    storageOpts.WithBuffer,
-		minimumBufferSize: storageOpts.WithMinimumBuffer,
 		currentOffset: 0,
 		bufferOffset:  0,
 	}