roadmap: remove description of implementation of garbage collector.

It was speculation.
Also replace one silly word with an English replacement.

R=golang-dev, bradfitzgo
CC=golang-dev
https://golang.org/cl/4339041

doc/contrib.html

@@ -49,7 +49,7 @@ systems and architectures.</p>
 <p>Features and ideas being developed or discussed by the Go team.</p>
 
 <h3 id="release"><a href="devel/release.html">Release History</a></h3>
-<p>A summarization of the changes between tagged releases of Go.</p>
+<p>A summary of the changes between tagged releases of Go.</p>
 
 <h3 id="golang-dev"><a href="http://groups.google.com/group/golang-dev">Developer Mailing List</a></h3>
 <p>The <a href="http://groups.google.com/group/golang-dev">golang-dev</a>

doc/devel/roadmap.html

@@ -37,8 +37,7 @@ Implementation roadmap</h3>
 
 <ul>
 <li>
-Improved garbage collector, most likely a reference counting collector
-with a cycle detector running in a separate core.
+Improved garbage collector.
 <li>
 Debugger.
 <li>