Remove `EccInstructions::NonIdentityPoint: TryFrom<Self::Point>` bound

After the previous commit, this is no longer used anywhere. Additionally
it was not enforcing the conversion in the circuit, which could lead to
circuit implementation mistakes.

src/circuit/gadget/ecc.rs

@@ -1,6 +1,5 @@
 //! Gadgets for elliptic curve operations.
 
-use std::convert::{TryFrom, TryInto};
 use std::fmt::Debug;
 
 use halo2::{
@@ -38,7 +37,7 @@ pub trait EccInstructions<C: CurveAffine>: Chip<C::Base> + UtilitiesInstructions
     /// Variable representing an elliptic curve point.
     type Point: From<Self::NonIdentityPoint> + IsIdentity + Clone + Debug;
     /// Variable representing a non-identity elliptic curve point.
-    type NonIdentityPoint: TryFrom<Self::Point> + Clone + Debug;
+    type NonIdentityPoint: Clone + Debug;
     /// Variable representing the affine short Weierstrass x-coordinate of an
     /// elliptic curve point.
     type X: Clone + Debug;
@@ -283,24 +282,6 @@ impl<C: CurveAffine, EccChip: EccInstructions<C> + Clone + Debug + Eq>
     }
 }
 
-impl<C: CurveAffine, EccChip: EccInstructions<C> + Clone + Debug + Eq> TryFrom<Point<C, EccChip>>
-    for NonIdentityPoint<C, EccChip>
-{
-    type Error = Error;
-
-    fn try_from(point: Point<C, EccChip>) -> Result<Self, Self::Error> {
-        point
-            .inner
-            .clone()
-            .try_into()
-            .map(|inner| Self {
-                chip: point.chip,
-                inner,
-            })
-            .map_err(|_| Error::SynthesisError)
-    }
-}
-
 /// An elliptic curve point over the given curve.
 #[derive(Copy, Clone, Debug)]
 pub struct Point<C: CurveAffine, EccChip: EccInstructions<C> + Clone + Debug + Eq> {

src/circuit/gadget/ecc/chip.rs

@@ -1,5 +1,3 @@
-use std::convert::TryFrom;
-
 use super::{EccInstructions, IsIdentity};
 use crate::{
     circuit::gadget::utilities::{
@@ -129,20 +127,6 @@ impl From<NonIdentityEccPoint> for EccPoint {
     }
 }
 
-impl TryFrom<EccPoint> for NonIdentityEccPoint {
-    type Error = Error;
-
-    fn try_from(point: EccPoint) -> Result<Self, Self::Error> {
-        if point.is_identity() == Some(true) {
-            return Err(Error::SynthesisError);
-        }
-        Ok(NonIdentityEccPoint {
-            x: point.x,
-            y: point.y,
-        })
-    }
-}
-
 /// Configuration for the ECC chip
 #[derive(Clone, Debug, Eq, PartialEq)]
 #[allow(non_snake_case)]