Move string.h to internal code
diff --git a/src/core/surface/completion_queue.c b/src/core/surface/completion_queue.c
index 652f23e..e1cc114 100644
--- a/src/core/surface/completion_queue.c
+++ b/src/core/surface/completion_queue.c
@@ -37,13 +37,13 @@
#include <string.h>
#include "src/core/iomgr/pollset.h"
+#include "src/core/support/string.h"
#include "src/core/surface/call.h"
#include "src/core/surface/event_string.h"
#include "src/core/surface/surface_trace.h"
#include <grpc/support/alloc.h>
#include <grpc/support/atm.h>
#include <grpc/support/log.h>
-#include <grpc/support/string.h>
#define NUM_TAG_BUCKETS 31