docs: remove deprecated difficulty check comment (#17781)

crates/ethereum/consensus/src/lib.rs

@@ -220,8 +220,6 @@ where
 
         validate_against_parent_timestamp(header.header(), parent.header())?;
 
-        // TODO Check difficulty increment between parent and self
-        // Ace age did increment it by some formula that we need to follow.
         self.validate_against_parent_gas_limit(header, parent)?;
 
         validate_against_parent_eip1559_base_fee(