Remove redundant fsync for WAL

[mrkm4ntr]

Because the hard state is already on disk after invocation of wal.Save.

etcd/server/wal/wal.go

Lines 937 to 944 in 71934ff

	if curOff < SegmentSizeBytes {
	if mustSync {
	return w.sync()
	}
	return nil
	}
	return w.cut()

etcd/server/wal/wal.go

Line 713 in 71934ff

if err := w.sync(); err != nil {

I've already checked with steps to reproduce of #10219 and there is no problem.

[ptabor]

Can you, please, sync with @brk0v whether the fix is really unneeded. I have limited trust to failpoints based tests to be (still) working.

[mrkm4ntr]

@brk0v, @jpbetz Could you take a look at this?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.