Remove 8-bit support from documentation

We removed support in the code ages ago, but overlooked this part of the
documentation. Also remove some dead code in Xvnc on the same theme.

unix/xserver/hw/vnc/Xvnc.man

@@ -37,15 +37,13 @@ Specify the size of the desktop to be created. Default is 1024x768.
 .TP
 .B \-depth \fIdepth\fP
 Specify the pixel depth in bits of the desktop to be created. Default is 24,
-other possible values are 8, 15, and 16 - anything else is likely to cause
-strange behaviour by applications.
+other possible values are 16 and 32. Anything else is likely to cause strange
+behaviour by applications and may prevent the server from starting at all.
 .
 .TP
 .B \-pixelformat \fIformat\fP
-Specify pixel format for server to use (BGRnnn or RGBnnn).  The default for
-depth 8 is BGR233 (meaning the most significant two bits represent blue, the
-next three green, and the least significant three represent red), the default
-for depth 16 is RGB565 and for depth 24 is RGB888.
+Specify pixel format for server to use (BGRnnn or RGBnnn). The default for
+depth 16 is RGB565 and for depth 24 and 32 is RGB888.
 .
 .TP
 .B \-interface \fIIP address\fP

unix/xserver/hw/vnc/xvnc.c

@@ -1577,16 +1577,6 @@ vfbScreenInit(ScreenPtr pScreen, int argc, char **argv)
     miSetPixmapDepths();
 
     switch (pvfb->fb.depth) {
-    case 8:
-	miSetVisualTypesAndMasks (8,
-				  ((1 << StaticGray) |
-				  (1 << GrayScale) |
-				  (1 << StaticColor) |
-				  (1 << PseudoColor) |
-				  (1 << TrueColor) |
-				  (1 << DirectColor)),
-				  8, PseudoColor, 0, 0, 0);
-	break;
     case 16:
 	miSetVisualTypesAndMasks (16,
 				  ((1 << TrueColor) |