doc: remove pull-requests.md preamble

Refs: nodejs/TSC#864 (comment)

PR-URL: #36960
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

doc/guides/contributing/pull-requests.md

@@ -1,10 +1,5 @@
 # Pull Requests
 
-There are two fundamental components of the Pull Request process: one concrete
-and technical, and one more process oriented. The concrete and technical
-component involves the specific details of setting up your local environment
-so that you can make the actual changes. This is where we will start.
-
 * [Dependencies](#dependencies)
 * [Setting up your local environment](#setting-up-your-local-environment)
   * [Step 1: Fork](#step-1-fork)