GitHub: Remove feature request placeholder template

We now have a proper link to godotengine/godot-proposals thanks to
#39019 and #39132, so that hacky 'Don't open issues here' template
is no longer needed.

.github/ISSUE_TEMPLATE/feature---enhancement-request.md

@@ -1,19 +0,0 @@
----
-name: Feature / Enhancement Request
-about: Adding new features or improving existing ones.
-title: 'IMPORTANT: This repository no longer accepts feature / enhancement requests.'
-labels: ''
-assignees: ''
-
----
-
-**IMPORTANT, PLEASE READ**
-
-Feature / Enhancement requests are no longer accepted in the main Godot repository.
-Please open an item by filling the relevant fields in the *Proposals* repository:
-
-https://github.com/godotengine/godot-proposals/issues/new/choose
-
-Do not submit to this repository or your issue will be closed.
-
-**IMPORTANT, PLEASE READ**