Update PULL_REQUEST_TEMPLATE.md

Most docs changes don't need testing. If they do, we can ask then.

Author: dead-claudia

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,8 +9,3 @@
 ## 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. -->
-
-## 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. -->