core: simplify pull request template

Author: tigitz

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,33 +1,6 @@
-<!--- Provide a general summary of your changes in the Title above -->
-
 ## Description
+<!-- Describe your changes in detail -->
 
-Describe your changes in detail.
-
-## Motivation and context
-
-Why is this change required? What problem does it solve?
-
-If it fixes an open issue, please link to the issue here (if you write `fixes #num`
-or `closes #num`, the issue will be automatically closed when the pull is accepted.)
-
-## How has this been tested?
-
-Please describe in detail how you tested your changes.
-
-Include details of your testing environment, and the tests you ran to
-see how your change affects other areas of the code, etc.
-
-## Screenshots (if appropriate)
-
-## Checklist:
-
-Go over all the following points before making your PR:
-
-- [ ] I have read the **[CONTRIBUTING](CONTRIBUTING.md)** document.
-- [ ] My pull request addresses exactly one patch/feature.
-- [ ] I have created a branch for this patch/feature.
-- [ ] I have added tests to cover my changes.
-- [ ] If my change requires a change to the documentation, I have updated it accordingly.
-
-If you're unsure about any of these, don't hesitate to ask. We're here to help!
+## Context
+<!-- Why is this change required? What problem does it solve? -->
+<!-- If it fixes an open issue, please link to the issue here (`fixes #num`) -->