change root lock to a non-recursive mutex
change root lock to a non-recursive mutex

Test Plan: first I switched it to an error checking mutex:

```
$ git diff
diff --git a/root.c b/root.c
index dbf5d95..bbca8c0 100644
--- a/root.c
+++ b/root.c
@@ -268,7 +268,7 @@ static w_root_t *w_root_new(const char *path, char **errmsg)
   root->refcnt = 1;
   w_refcnt_add(&live_roots);
   pthread_mutexattr_init(&attr);
-  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
   pthread_mutex_init(&root->lock, &attr);
   pthread_mutexattr_destroy(&attr);
```

this passed the integration tests; the move to add w_query_execute_locked was what I think removed this dependency.

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