cs & thread: remove redundant internal atomically

racket/src/thread/schedule.rkt

@@ -242,7 +242,7 @@
 
 ;; ----------------------------------------
 
-;; Have we tried all threads without since most recently making
+;; Have we tried all threads since most recently making
 ;; progress on some thread?
 (define (all-threads-poll-done?)
   (= (hash-count poll-done-threads)

racket/src/thread/thread-group.rkt

@@ -72,9 +72,9 @@
     (set-thread-group-chain! tg (node-next n))
     (node-child n)]))
 
+;; In atomic mode:
 (define (thread-group-add! parent child)
-  (atomically
-   (let loop ([parent parent] [child child])
+  (assert-atomic-mode)
   ;; Adding to the start of the group tends to reverse the schedule
   ;; order, but it also avoids a problem where two threads that
   ;; both loop and `sleep` (which deschedules and reschedules) take
@@ -97,11 +97,11 @@
     ;; added child to formerly empty parent => add the parent
     (define parent-parent (thread-group-parent parent))
     (when parent-parent
-         (loop parent-parent parent))))))
+      (thread-group-add! parent-parent parent))))
 
+;; In atomic mode:
 (define (thread-group-remove! parent child)
-  (atomically
-   (let loop ([parent parent] [child child])
+  (assert-atomic-mode)
   (define n (child-node child))
   (when (or (eq? (node-prev n) 'none)
             (eq? (node-next n) 'none))
@@ -122,7 +122,7 @@
     ;; parent thread group is now empty, so remove it, too
     (define parent-parent (thread-group-parent parent))
     (when parent-parent
-         (loop parent-parent parent))))))
+      (thread-group-remove! parent-parent parent))))
 
 (define (thread-group-all-threads parent accum)
   (cond