Remove unnecessary context from some util functions.

src/parser/horizontal_rule.rs

@@ -19,7 +19,7 @@ pub fn horizontal_rule<'r, 's>(
     context: Context<'r, 's>,
     input: OrgSource<'s>,
 ) -> Res<OrgSource<'s>, HorizontalRule<'s>> {
-    start_of_line(context, input)?;
+    start_of_line(input)?;
     let (remaining, rule) = recognize(tuple((
         space0,
         verify(many1_count(tag("-")), |dashes| *dashes >= 5),