Moved grayscale toggle code from C to ASM; enabled grayscale toggle in dos port

zsnes/src/win/winlink.cpp

@@ -1476,8 +1476,6 @@ void Stop36HZ(void)
 
 char WinMessage[256];
 extern unsigned char cvidmode;
-extern BYTE GrayscaleMode;
-extern BYTE V8Mode;
 DWORD FirstVid=1;
 DWORD FirstFull=1;
 extern BYTE GUIWFVID[];
@@ -1492,8 +1490,6 @@ void initwinvideo(void)
    RECT rc1, swrect;
    DWORD newmode=0;
 
-   V8Mode = (GrayscaleMode == 1);
-
    if (CurMode!=cvidmode)
    {
       CurMode=cvidmode;