Resolve some MSVC warnings

src/conio/win32cio.c

@@ -801,7 +801,7 @@ void win32_textmode(int mode)
 	COORD	sz;
 	SMALL_RECT	rc;
 	CONSOLE_SCREEN_BUFFER_INFOEX	bi;
-	int i;
+	size_t i;
 	DWORD oldmode;
 	DWORD cmode;
 	int wx, wy;

src/conio/win32gdi.c

@@ -686,8 +686,6 @@ gdi_handle_getdpiscaledsize(WORD dpi, LPSIZE sz)
 static LRESULT
 gdi_handle_wm_activateapp(WPARAM wParam, LPARAM lParam)
 {
-	int w, h;
-
 	if (wParam == FALSE) {
 		if (fullscreen) {
 			// Minimize when we lose focus in fullscreen