nixos-install manual: remove --chroot option

This option has been removed from the tool in favour of nixos-enter.

(cherry picked from commit 152454d)

nixos/doc/manual/man-nixos-install.xml

@@ -57,9 +57,6 @@
     <arg>
       <arg choice='plain'><option>--show-trace</option></arg>
     </arg>
-    <arg>
-      <arg choice='plain'><option>--chroot</option></arg>
-    </arg>
     <arg>
       <arg choice='plain'><option>--help</option></arg>
     </arg>
@@ -177,14 +174,6 @@ it.</para>
     </listitem>
   </varlistentry>
 
-  <varlistentry>
-    <term><option>--chroot</option></term>
-    <listitem>
-      <para>Chroot into given installation. Any additional arguments passed are going to be executed inside the chroot.
-      </para>
-    </listitem>
-  </varlistentry>
-
   <varlistentry>
     <term><option>--help</option></term>
     <listitem>