Update obsolete comment.

Author: J. Cliff Dyer

src/clang.rs

@@ -349,9 +349,7 @@ impl Cursor {
 
     /// Get the signed constant value for this cursor's enum variant referent.
     ///
-    /// Returns `LLONG_MIN` if the cursor's referent is not an enum variant,
-    /// which is also a valid enum value, so callers should check the cursor
-    /// kind before calling this method (see issue #127).
+    /// Returns None if the cursor's referent is not an enum variant.
     pub fn enum_val_signed(&self) -> Option<i64> {
         unsafe {
             if self.kind() == CXCursor_EnumConstantDecl {