spec: remove sentence discussing existing implementations

Fixes #22282.

Change-Id: I4097e9cbd590ab6c8b1511a3b752c6ac98ac819b
Reviewed-on: https://go-review.googlesource.com/72792
Reviewed-by: Rob Pike <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>

Author: griesemer

doc/go_spec.html

@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of October 19, 2017",
+	"Subtitle": "Version of October 23, 2017",
 	"Path": "/ref/spec"
 }-->
 
@@ -16,8 +16,7 @@ <h2 id="Introduction">Introduction</h2>
 in mind. It is strongly typed and garbage-collected and has explicit
 support for concurrent programming.  Programs are constructed from
 <i>packages</i>, whose properties allow efficient management of
-dependencies. The existing implementations use a traditional
-compile/link model to generate executable binaries.
+dependencies.
 </p>
 
 <p>