Fix inconsistencies

docs/tezos-basics/nodes/nodes.md:

• Archive node size: to update
• Giganode link: dead link

docs/tezos-basics/liquid-proof-of-stake/liquid-proof-of-stake.md:

• PoS link: wrong link
• 51% attack link: dead link + two references on same line
• LPoS: roll is an outdated concept
• LPoS security: not sure to understand