Don't expose private sig parse method via try_from

src/sig.rs

@@ -12,13 +12,6 @@ pub struct Sig<'a> {
 	pub sig: Cow<'a, str>,
 }
 
-impl<'a> TryFrom<&'a str> for Sig<'a> {
-	type Error = ParsingError<'a>;
-
-	fn try_from(value: &'a str) -> ParsingResult<Self> {
-		Sig::parse(value)
-	}
-}
 // Neither the parse nor the serializa method is public since
 // it doesn't really make sense to de/serialize the
 // sig into the narinfo format outside of de/serializing a whole narinfo