Update tile-rows help message

Updated tile-rows help message since multi-thread support was already
added.

Change-Id: Ie701b026ab251ac17bb632730dde67406124f9ec

apps/aomenc.c

diff --git a/apps/aomenc.c b/apps/aomenc.c
index 25f012f..3e4b059 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -426,8 +426,7 @@
 static const arg_def_t tile_cols =
     ARG_DEF(NULL, "tile-columns", 1, "Number of tile columns to use, log2");
 static const arg_def_t tile_rows =
-    ARG_DEF(NULL, "tile-rows", 1,
-            "Number of tile rows to use, log2 (set to 0 while threads > 1)");
+    ARG_DEF(NULL, "tile-rows", 1, "Number of tile rows to use, log2");
 static const arg_def_t tile_width =
     ARG_DEF(NULL, "tile-width", 1, "Tile widths (comma separated)");
 static const arg_def_t tile_height =