Remove "Legacy key" part from Handbook

[os11k]

I propose to remove "Legacy key" part from Operate a Stake Pool - Handbook. Do we still need it there?

I found that on 3 pages. 2 of them are in Handbook, so I'm pretty sure nobody needs legacy keys at least for creating a pool. No? If this is ok, I will create PR.

[katomm]

This issue is open for a while now, does anyone else have any opinions on this?

[rdlrt]

I agree with OP (a very unlikely scenario, but if anyone who does need it has other ways to do so)

[katomm]

Since Priyank has confirmed, I am confident it can be removed. Would be great if you can do that @os11k

[os11k]

Hi! I'm bit busy this week, I will try to work on this next week on during weekend. Cheers!

[katomm]

No rush, sir.