Remove duplicate bug report issue template

The bug report issue template is duplicated (`bug-report.md` and
`bug_report.md`, note the `-`/`_` difference).

Thus, GitHub was unable to use the bug report issue template, and it
does not show up when a new issue is being created.

Let's remove the duplicate template `bug_report.md`.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,34 +0,0 @@
----
-name: Bug report
-about: Create a report to help us improve
-title: 'Bug report: <Insert title here>'
-labels: bug
-assignees: ''
-
----
-
-<!-- Prefix the title above with 'Bug report:' -->
-**Describe the bug**
-A clear and concise description of what the bug is.
-
-**To Reproduce**
-Steps to reproduce the behavior or a link to the recipe / input used to cause the bug:
-
-1. Go to '...'
-2. Click on '....'
-3. Scroll down to '....'
-4. See error
-
-**Expected behavior**
-A clear and concise description of what you expected to happen.
-
-**Screenshots**
-If applicable, add screenshots to help explain your problem.
-
-**Desktop (if relevant, please complete the following information):**
- - OS: [e.g. Windows] 
- - Browser [e.g. chrome, safari]
- - Version [e.g. 22]
-
-**Additional context**
-Add any other context about the problem here.