Remove redundant instructions from PR template

Author: hugovk

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,15 +1,5 @@
 Subject: <short purpose of this pull request>
 
-<!--
-  Before posting a pull request, please choose a appropriate branch:
-
-  - Breaking changes: master
-  - Critical or severe bugs: X.Y.Z
-  - Others: X.Y
-
-  For more details, see https://www.sphinx-doc.org/en/master/internals/release-process.html#branch-model
--->
-
 ### Feature or Bugfix
 <!-- please choose -->
 - Feature