Update label applied for performance template bugs (#41717)

.github/ISSUE_TEMPLATE/performance.md

 ---
-name: I have a performance problem with my application
+name: My app is slow or missing frames.
 about: You are writing an application but have discovered that it is slow, you are
   not hitting 60Hz, or you are getting jank (missed frames).
 title: ''
-labels: 'severe: performance'
+labels: 'created via performance template'
 assignees: ''
 
 ---