Simplify syntax-path API to use integer-only indices

.gitignore

@@ -1,6 +1,7 @@
 compiled/
 doc/
 *~
+*.backup
 # These only come up if you generate the scribble docs manually, instead of
 # through `raco setup`. But we exclude them anyway to help newcomers (and
 # Copilot) avoid accidentally committing rendered documentation files.

private/syntax-movement.rkt

@@ -91,6 +91,6 @@
 
        ; void
        (syntax-path (list 3 0))
-       (sorted-set (syntax-path (list 3 2 (tail-syntax 1) 0)) #:comparator syntax-path<=>)))
+       (sorted-set (syntax-path (list 3 2 1)) #:comparator syntax-path<=>)))
 
     (check-equal? table expected-table)))