Fixup the github pull request template
When creating a single commit PR, github will now automatically
include the commit comment first in the pull request description, and
add the template content last.  That makes the description section at
the end useless.
<!--
-Thank you for your pull request. Please review below requirements.
+Thank you for your pull request. Please review these requirements:
Contributors guide: https://github.com/openssl/openssl/blob/master/CONTRIBUTING
+
+Other than that, provide a description above this comment if there isn't one already, and if it fixes a github issue, add 'Fixes #XXXX' (without quotes) as well.
-->
##### Checklist
<!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->
- [ ] documentation is added or updated
- [ ] tests are added or updated
-
-##### Description of change
-<!-- Provide a description of the changes.
-
-If it fixes a github issue, add Fixes #XXXX.
--->
