Update pull_request_template.md

Since approval is mandatory there is no need of that item

Author: CarloLucibello

.github/pull_request_template.md

@@ -9,4 +9,3 @@ the right direction since it can be hard to change later.]
 - [ ] Tests are added
 - [ ] Entry in NEWS.md
 - [ ] Documentation, if applicable
-- [ ] API changes require approval from a committer (different from the author, if applicable)