chore: remove sentinel which is not needed since Dash Core v20

[knst]

trafficstars

Since Dash Core v20 no more sentinel is needed:

• https://www.dash.org/blog/dashcore-v20-0-product-brief/
• https://github.com/dashpay/dash/blob/v20.0.0/doc/release-notes.md#sentinel-deprecation

[QuantumExplorer]

@Bertrand256 can we get this merged in?

[Bertrand256]

My apologies, I must have missed that. In the meantime I've been making my own changes to the ansible Dash node installation script, so I'll merge them together in the coming days.