Delegate method assist doesn't fix up `Self` references

[Veykril]

struct Struct {
    field$0: u8,
}

produces

impl Struct {
    pub fn saturating_mul(self,rhs:Self) ->Self {
        self.field.saturating_mul(rhs)
    }
}

when it should produce

impl Struct {
    pub fn saturating_mul(self,rhs:u8) ->u8{
        self.field.saturating_mul(rhs)
    }
}