xfree86: Man page shouldn't say Device is mandatory anymore

man xorg.conf states that the 'Device' identifier is required in the
'Screen' section, yet current xserver defaults properly and boots up
fine without it.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=20742Signed-off-by: Bryce Harrington <bryce@canonical.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

hw/xfree86/man/xorg.conf.man

@@ -1821,9 +1821,7 @@ sections have the following format:
 .PP
 The
 .B Identifier
-and
-.B Device
-entries are mandatory.
+entry is mandatory.
 All others are optional.
 .PP
 The
@@ -1841,11 +1839,10 @@ The entries available
 for this section are:
 .TP 7
 .BI "Device  \*q" device\-id \*q
-This mandatory entry specifies the
+This entry specifies the
 .B Device
-section to be used for this screen.
-This is what ties a specific graphics card to a screen.
-The
+section to be used for this screen.  When multiple graphics cards are
+present, this is what ties a specific card to a screen.  The
 .I device\-id
 must match the
 .B Identifier