Remove the old issue template

We have separate templates for bug reports and feature requests now.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

.github/issue_template.md

@@ -1,46 +0,0 @@
-_Note:_ this is a template, please remove the parts that are not
-applicable (these initial notes, and the "Bug" section for a Feature request
-and vice-versa).
-
-**Note:** to report a security vulnerability, see
-[SECURITY.md](../SECURITY.md). Please do not use github issues for
-vulnerabilities.
-
-_Note:_ to get support, see [SUPPORT.md](../SUPPORT.md). Please do not use
-github issues for questions.
-
----------------------------------------------------------------
-### Description
-- Type: Bug | Enhancement / Feature Request
-- Priority: Blocker | Major | Minor
-
----------------------------------------------------------------
-## Bug
-
-**OS**  
-Mbed OS|linux|windows|
-
-**mbed TLS build:**  
-Version: x.x.x or git commit id  
-OS version: x.x.x  
-Configuration: please attach config.h file where possible  
-Compiler and options (if you used a pre-built binary, please indicate how you obtained it):  
-Additional environment information:  
-
-**Peer device TLS stack and version**  
-OpenSSL|GnuTls|Chrome|NSS(Firefox)|SecureChannel (IIS/Internet Explorer/Edge)|Other  
-Version:  
-
-**Expected behavior**   
-
-**Actual behavior**  
-
-**Steps to reproduce**  
-
-----------------------------------------------------------------
-## Enhancement / Feature Request
-
-**Suggested enhancement**  
-
-**Justification - why does the library need this feature?**  
-