Use separate pull requests templates for each of GitHub and Gitea.

.github/pull_request_template.md

@@ -2,9 +2,7 @@
 
 Thanks for your contribution! 
 
-If you're submitting this PR on **projects.torsion.org**: Please ignore the following. You can safely delete this text before submitting your PR.
-
-If you're submitting this PR on **GitHub**: Unfortunately, we don't use GitHub pull requests to manage code contributions to this repository (and GitHub doesn't have any way to disable pull requests entirely). Instead, please see:
+Unfortunately, we don't use GitHub pull requests to manage code contributions to this repository (and GitHub doesn't have any way to disable pull requests entirely). Instead, please see:
 
 https://torsion.org/borgmatic/#contributing