cursor: drop ARGB_CURSOR

I doubt anyone builds with this turned off or has done for a long
time.

It helps my eyes bleed slightly less when reading the code, I've left
the define in place as some drivers use it.

Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/cursorstr.h

@@ -64,9 +64,7 @@ typedef struct _CursorBits {
     unsigned short width, height, xhot, yhot;   /* metrics */
     int refcnt;                 /* can be shared */
     PrivateRec *devPrivates;    /* set by pScr->RealizeCursor */
-#ifdef ARGB_CURSOR
     CARD32 *argb;               /* full-color alpha blended */
-#endif
 } CursorBits, *CursorBitsPtr;
 
 #define CURSOR_BITS_SIZE (sizeof(CursorBits) + dixPrivatesSize(PRIVATE_CURSOR_BITS))