fix issue templates + remove task list from PR template (#1050)

### Problem

I noticed yesterday when creating issues that the form templates
introduced by #1040 aren't showing up.
Also, I think the task list at the end of the PR template isn't very
useful, creates unnecessary visual noise in the PR descriptions, and
might discourage people from posting PRs.

### Solution

The cause of the forms not showing was that I put them in the wrong
folder. This PR fixes the path of the files and removes the task list at
the end of the PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -22,9 +22,3 @@ Add any important additional information as bullet points, such as:
 - Open questions and concerns
 - Limitations
 -->
-
-### Checklist
-
-- [ ] Unit test all changes
-- [ ] Update scaladocs if needed
-- [ ] Update the README if needed