Issue template: Remove checkbox and reword some comments

Author: akien-mga

ISSUE_TEMPLATE.md

@@ -1,9 +1,13 @@
+<!-- Please search existing issues for potential duplicates before filing yours:
+https://github.com/godotengine/godot/issues?q=is%3Aissue
+-->
+
 **Godot version:**
-<!-- If thirdparty or self-compiled, specify the build date or commit hash. -->
+<!-- Specify commit hash if non-official. -->
 
 
 **OS/device including version:**
-<!-- If graphics related, specify also GPU model and drivers. -->
+<!-- Specify GPU model and drivers if graphics-related. -->
 
 
 **Issue description:**
@@ -14,7 +18,4 @@
 
 
 **Minimal reproduction project:**
-<!-- Optional but greatly speeds up debugging. You can drag and drop a zip archive to upload it. -->
-
-
-- [ ] I searched the existing [GitHub issues](https://github.com/godotengine/godot/issues?utf8=%E2%9C%93&q=is%3Aissue+) for potential duplicates.
+<!-- Recommended as it greatly speeds up debugging. Drag and drop a zip archive to upload it. -->