Update issue templates (#699)

Author: petea

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,12 +1,12 @@
 ---
 name: Bug report
 about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
 
 ---
 
-**Are you filing an issue about iOS 12?**
-You can find preliminary support for iOS 12 in the (ios12beta branch)[https://github.com/openid/AppAuth-iOS/tree/ios12beta] and background information in (the associated pull request)[https://github.com/openid/AppAuth-iOS/pull/246]. Please review these materials before filing iOS 12 issues. Thanks.
-
 **Describe the bug**
 A clear and concise description of what the bug is.
 

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,12 +1,12 @@
 ---
 name: Feature request
 about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
 
 ---
 
-**Are you filing an issue about iOS 12?**
-You can find preliminary support for iOS 12 in the (ios12beta branch)[https://github.com/openid/AppAuth-iOS/tree/ios12beta] and background information in (the associated pull request)[https://github.com/openid/AppAuth-iOS/pull/246]. Please review these materials before filing iOS 12 issues. Thanks.
-
 **Is your feature request related to a problem? Please describe.**
 A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]