chore: remove plunker from issue template (#9614)

Author: jelbourn

.github/ISSUE_TEMPLATE.md

@@ -8,9 +8,8 @@
 
 
 #### What are the steps to reproduce?
-Providing a StackBlitz/Plunker (or similar) is the *best* way to get the team to see your issue. <br/>
-Plunker starter (using on `@master`): https://goo.gl/uDmqyY<br/>
-StackBlitz starter (using latest `npm` release): https://goo.gl/wwnhMV<br/>
+Providing a StackBlitz reproduction is the *best* way to share your issue. <br/>
+StackBlitz starter: https://goo.gl/wwnhMV<br/>
 
 
 #### What is the use-case or motivation for changing an existing behavior?