dev-manual, ref-manual: Replaced ‐‐ with "--"

Fixes [YOCTO #7386]

Apparently, copying HTML displayed commands that have a
double dash created through "‐‐" in the docbook source
causes some issues in the shell.  I have scrubbed the manual set
to replace any "‐‐" strings with "--".

Reported-by: Paul Eggleton <paul.eggleton@intel.com>
(From yocto-docs rev: e88b813b71d7d6d8acd8a8638f2db71265145b64)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/migration.xml

@@ -1014,7 +1014,7 @@
                     The <filename>buildhistory-diff</filename> and
                     <filename>buildhistory-collect-srcrevs</filename>
                     utilities have improved command-line handling.
-                    Use the <filename>&dash;&dash;help</filename> option for
+                    Use the <filename>--help</filename> option for
                     each utility for more information on the new syntax.
                     </para></listitem>
             </itemizedlist>
@@ -1730,7 +1730,7 @@
             The minimum
             <ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink> version required
             on the build host is now 1.7.8 because the
-            <filename>&dash;&dash;list</filename> option is now required by
+            <filename>--list</filename> option is now required by
             BitBake's Git fetcher.
             As always, if your host distribution does not provide a version of
             Git that meets this requirement, you can use the
@@ -1770,7 +1770,7 @@
                     class instead of the <filename>autotools</filename> class.
                     </para></listitem>
                 <listitem><para><emphasis>
-                    The <filename>&dash;&dash;foreign</filename> option is
+                    The <filename>--foreign</filename> option is
                     no longer passed to <filename>automake</filename> when
                     running <filename>autoconf</filename>:</emphasis>
                     This option tells <filename>automake</filename> that a