Use Latest Delegate for Minipools (RPIP-77)

## Summary Set minipools managed via Smart Node to use the latest delegate and remove supported Smart Node configuration options for setting older delegates. --- ## Rationale The goal is to improve protocol-wide consistency among minipools, enable pDAO approved minipool changes, and remove some technical blockers to future enforcement mechanisms. A non-trivial number of minipools are persistently underperforming, reducing overall rETH yield and harming demand. Reduced rETH demand complicates...