Adjust heading levels in github templates

Since the page contains an <h1> tag (the title of the issue), the main
headings of this file should be level 2 headings.

We're removing the "How" section in the flaky specs template for
simplicity (and because we usually don't use this template at all).

Note that MDL reports that the first heading should be a level 1
heading, but, as mentioned earlier, this doesn't make sense in the
context of a github issue. We'll probably exclude these files from MDL
checks in order to avoid this issue.

.github/ISSUE_TEMPLATE.md

@@ -1,12 +1,12 @@
-### User Story
+## User Story
 
 [comment]: # (As a <user type>, I want to <task> so that <goal>.)
 
-### Why is this Needed?
+## Why is this Needed?
 
 [comment]: # (Describe the problem and why this task is needed. Provide a description of the current state, what you would like to happen, and what actually happened)
 
-### Description
+## Description
 
 [comment]: # (Feature or Bug? eg. Type: Bug)
 *Type*:

.github/ISSUE_TEMPLATE/flakies.md

@@ -1,4 +1,4 @@
-# What
+## What
 
 Tests that fail randomly are called "flakies", this one seems to be one:
 
@@ -12,11 +12,6 @@ Tests that fail randomly are called "flakies", this one seems to be one:
   FILL_WITH_FAILURE_REPORT
 ```
 
-# How
-
-- [ ] Explain why the test is flaky, or under which conditions/scenario it fails randomly
-- [ ] Explain why your PR fixes it
-
 ## Tips for flaky hunting
 
 ### Random values issues