PR_TEMPLATE: Remove issue reference, description

Since the template gets added after the text from a single-commit pull
request, it seems to make more sense to just remove the issue reference
and description bits, as those should be included in the commit message
to begin with.

Author: mbland

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,8 +9,4 @@
 [gh-tos]:  https://help.github.com/articles/github-terms-of-service/#6-contributions-under-repository-license
 [license]: https://github.com/mbland/go-script-bash/LICENSE.md
 
-Closes #.
-
-Replace this paragraph with a description of the change.
-
 cc: @mbland