simplify github template with linear ticket link (#3455)

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,5 @@
-## Issue ID
-
-<!-- Fill in an issue ID or type "N/A" if there isn't one -->
-
+## POR-
+<!-- Enter your issue ID in the title above or type "N/A" if there isn't one -->
 ## What does this PR do?
 
 <!--