No issue: change label in perf issue template to `performance`

I recently changed the label from `eng:performance` to `performance`
so this template also has to be updated.

.github/ISSUE_TEMPLATE/---performance-issue.md

@@ -2,7 +2,7 @@
 name: "⌛ Performance issue"
 about: Create a performance issue if the app is slow or it uses too much memory, disk space, battery, or network data
 title: ""
-labels: "eng:performance"
+labels: "performance"
 assignees: ''
 
 ---