[mojo] Clean up doc

Delete words that are no longer true.

BUG=
TBR=benwells@chromium.org

Review URL: https://codereview.chromium.org/1642023003 .

Cr-Commit-Position: refs/heads/master@{#372100}

docs/mojo_in_chromium.md

 # Mojo in Chromium
 
 This document is intended to serve as a Mojo primer for Chromium developers. No
-prior knowledge of Mojo is assumed, but you should have a decent grasp of C++
-and be familiar with Chromium's multi-process architecture as well as common
-concepts used throughout Chromium such as smart pointers, message loops,
-callback binding, and so on.
+prior knowledge of Mojo is assumed.
 
 [TOC]