Remove TODO for ROI

Implementation with tests was merged in here:
https://aomedia-review.googlesource.com/c/aom/+/200061

Change-Id: Id3b9bd15f39c82f966b8a4065e9ff74873a7bf2f

aom/aomcx.h

diff --git a/aom/aomcx.h b/aom/aomcx.h
index a0b0fe4..ee36ab0 100644
--- a/aom/aomcx.h
+++ b/aom/aomcx.h
@@ -1633,9 +1633,6 @@
 /*!\brief  aom region of interest map
  *
  * These defines the data structures for the region of interest map
- *
- * TODO(yaowu): create a unit test for ROI map related APIs
- *
  */
 typedef struct aom_roi_map {
   /*! If ROI is enabled. */