Revert "Test case for #5626 (#8204)" (#8206)

This reverts commit c7cc934632.

tests/threads/t5626.nim

@@ -1,27 +0,0 @@
-import threadpool
-
-var ch: Channel[int]
-ch.open
-var pch = ch.addr
-
-proc run(f: proc(): int {.gcsafe.}): proc() =
-  let r = spawn f()
-  return proc() = await(r)
-
-var working = false
-
-proc handler(): int =
-  while true:
-    let (h, v) = pch[].tryRecv()
-    if not h:
-      discard cas(working.addr, true, false)
-      break
-  1
-
-proc send(x: int) =
-  ch.send(x)
-  if cas(working.addr, false, true):
-    discard run(handler)
-
-for x in 0..1000000:
-  send(x)