docs: remove outdated suggestion to make patches with "diff -urp"/"git diff"

I can't think of any good reason to do either of those, and having the
examples there will just lead to unusable patch emails from people who
can't be bothered to read the entire page.

HACKING

@@ -23,19 +23,11 @@ libvirt-python) online <http://libvirt.org/git/>.
 join the appropriate language team. The libvirt release process automatically
 pulls the latest version of each translation file from zanata.
 
-(4) Post patches in unified diff format, with git rename detection enabled. You
+(4) Post patches using "git send-email", with git rename detection enabled. You
 need a one-time setup of:
 
   git config diff.renames true
 
-After that, a command similar to this should work:
-
-  diff -urp libvirt.orig/ libvirt.modified/ > libvirt-myfeature.patch
-
-or:
-
-  git diff > libvirt-myfeature.patch
-
 Also, for code motion patches, you may find that "git diff --patience"
 provides an easier-to-read patch. However, the usual workflow of libvirt
 developer is:

docs/hacking.html.in

@@ -23,20 +23,10 @@
         automatically pulls the latest version of each translation
         file from zanata.</li>
 
-      <li><p>Post patches in unified diff format, with git rename
+      <li><p>Post patches using "git send-email", with git rename
         detection enabled.  You need a one-time setup of:</p>
 <pre>
   git config diff.renames true
-</pre>
-        <p>After that, a command similar to this should work:</p>
-<pre>
-  diff -urp libvirt.orig/ libvirt.modified/ &gt; libvirt-myfeature.patch
-</pre>
-        <p>
-          or:
-        </p>
-<pre>
-  git diff &gt; libvirt-myfeature.patch
 </pre>
         <p>Also, for code motion patches, you may find that <code>git
         diff --patience</code> provides an easier-to-read patch.