DOCS: Remove Issue Templates (#849)

These are now implemented centrally in the executablebooks/.github repo

.github/ISSUE_TEMPLATE/bug_report.md

----
-name: Bug report 🐛
-about: Create a report to help us improve
-title: ''
-labels: bug
-assignees: ''
-
----
-
-**Describe the bug**
-A clear and concise description of what the bug is.
-
-**To Reproduce**
-Steps to reproduce the behavior:
-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.
-
-A link to your book's repository.
-
-If relevant, a minimal example of the input text should be supplied,
-together with a screen-shot of the output book document and/or command-line output, e.g.
-
-```markdown
-some text...
-```
-
-```console
-$ jupyter-book build mybook
-ERROR ...
-```
-
-**Environment (please complete the following information):**
- - Python Version [e.g. 3.7.1]
- - Output of `jupyter-book --version`
-
-**Additional context**
-Add any other context about the problem here.

.github/ISSUE_TEMPLATE/documentation-improvements.md

----
-name: Documentation Improvements 📚
-about: Suggest improvements to the documentation
-title: ''
-labels: documentation
-assignees: ''
-
----
-
-**Is your feature request related to a problem? Please describe.**
-A clear and concise description of what the problem is. Ex. This section is unclear [...]
-
-**A link to the documentation page where you see an issue.**
-E.g., https://jupyterbook.org/intro.html
-
-**Describe the solution you'd like**
-A clear and concise description of what you want to happen.

.github/ISSUE_TEMPLATE/feature_request.md

----
-name: Feature request 💡
-about: Suggest an idea for this project
-title: ''
-labels: enhancement
-assignees: ''
-
----
-
-**Is your feature request related to a problem? Please describe.**
-A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
-
-**Describe the solution you'd like**
-A clear and concise description of what you want to happen.
-
-**Describe alternatives you've considered**
-A clear and concise description of any alternative solutions or features you've considered.
-
-**Additional context**
-Add any other context or screenshots about the feature request here.

.gitignore

@@ -135,3 +135,6 @@ dmypy.json
 
 # VSCode config
 .vscode
+
+# OSX
+.DS_Store