doc: remove reference to bug count from install.html

Fixes #1574.

R=rsc, r2
CC=golang-dev
https://golang.org/cl/4240066

doc/install.html

@@ -163,8 +163,7 @@ The compiler is 6g.
 </pre>
 
 <p>
-where <var>N</var> is a number that varies from release to release
-and the details on the last few lines will reflect the operating system,
+where the details on the last few lines reflect the operating system,
 architecture, and root directory used during the install.
 </p>