remove subtitles from mock

Author: archmoj

test/image/baselines/zorder-overlayed-subplots-multiple-traces-main-subplot.png

@@ -43,10 +43,7 @@
  "layout": {
   "showlegend": true,
   "title": {
-   "text": "zorder overlayed subplots - multiple on the same subplot",
-   "subtitle": {
-    "text": "Orange trace is displayed on top!"
-   }
+   "text": "zorder overlayed subplots - multiple on the same subplot"
   },
   "width": 600,
   "height": 400,

test/image/baselines/zorder-overlayed-subplots-multiple-traces-main-subplot2.png

@@ -43,10 +43,7 @@
  "layout": {
   "showlegend": true,
   "title": {
-   "text": "zorder overlayed subplots - multiple on the same subplot",
-   "subtitle": {
-    "text": "Orange trace is displayed on top!"
-   }
+   "text": "zorder overlayed subplots - multiple on the same subplot"
   },
   "width": 600,
   "height": 400,