Revert issue template (#9345) -- it doesn't work

This reverts commit 18c84e0.

Author: gvanrossum

.github/ISSUE_TEMPLATE/bug.md

@@ -0,0 +1,20 @@
+Note: if you are reporting a wrong signature of a function or a class in
+the standard library, then the typeshed tracker is better suited
+for this report: https://github.com/python/typeshed/issues
+
+Please provide more information to help us understand the issue:
+
+* Are you reporting a bug, or opening a feature request?
+* Please insert below the code you are checking with mypy,
+  or a mock-up repro if the source is private. We would appreciate
+  if you try to simplify your case to a minimal repro.
+* What is the actual behavior/output?
+* What is the behavior/output you expect?
+* What are the versions of mypy and Python you are using?
+  Do you see the same issue after installing mypy from Git master?
+* What are the mypy flags you are using? (For example --strict-optional)
+* If mypy crashed with a traceback, please paste
+  the full traceback below.
+
+(You can freely edit this text, please remove all the lines
+you believe are unnecessary.)