spec: remove => (alias) operator from Operators and Delimiters section

(Revert of https://go-review.googlesource.com/#/c/32310/)

For #16339.
Fixes #17975.

Change-Id: I36062703c423a81ea1c5b00f4429a4faf00b3782
Reviewed-on: https://go-review.googlesource.com/33365Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go_spec.html

@@ -265,7 +265,7 @@ The following character sequences represent <a href="#Operators">operators</a>,
 *    ^     *=    ^=     &lt;-    &gt;     &gt;=    {    }
 /    &lt;&lt;    /=    &lt;&lt;=    ++    =     :=    ,    ;
 %    &gt;&gt;    %=    &gt;&gt;=    --    !     ...   .    :
-     &amp;^          &amp;^=    =&gt;
+     &amp;^          &amp;^=
 </pre>
 
 <h3 id="Integer_literals">Integer literals</h3>