media: vidtv: remove duplicate include in vidtv_psi

'string.h' included in 'vidtv_psi.c' is duplicated.
Signed-off-by: Zhang Yunkai <zhang.yunkai@zte.com.cn>
Acked-by: Daniel Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/test-drivers/vidtv/vidtv_psi.c

@@ -19,7 +19,6 @@
 #include <linux/ratelimit.h>
 #include <linux/slab.h>
 #include <linux/string.h>
-#include <linux/string.h>
 #include <linux/time.h>
 #include <linux/types.h>