doc: remove math/bits from 'minor changes' section

The new math/bits package has a section for itself, and should not be
mentioned in the 'Minor changes to the library' section of the release
notes.

Updates #20587

Change-Id: I13ecd35f5cee4324e50b2d31800e399c00159126
Reviewed-on: https://go-review.googlesource.com/45051Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.9.html

@@ -162,7 +162,7 @@ type T1 = T2
 
 <h3 id="math-bits">New bit manipulation package</h3>
 
-<p>
+<p> <!-- CL 36315 -->
   Go 1.9 includes a new package,
   <a href="/pkg/math/bits/"><code>math/bits</code></a>, with optimized
   implementations for manipulating bits. On most architectures
@@ -354,14 +354,6 @@ type T1 = T2
 
 </dl><!-- math/big -->
 
-<dl id="math/bits"><dt><a href="/pkg/math/bits/">math/bits</a></dt>
-  <dd>
-    <p><!-- CL 36315 -->
-      TODO: <a href="https://golang.org/cl/36315">https://golang.org/cl/36315</a>: added package for bit-level counting and manipulation
-    </p>
-
-</dl><!-- math/bits -->
-
 <dl id="mime/multipart"><dt><a href="/pkg/mime/multipart/">mime/multipart</a></dt>
   <dd>
     <p><!-- CL 39223 -->