dxva2: don't check for DXVA_PictureParameters->wDecodedPictureIndex

This structure is well defined by Microsoft at:
http://msdn.microsoft.com/en-us/library/windows/hardware/ff564012(v=vs.85).aspx
Thus, the wDecodedPictureIndex member is guaranteed to exist.

Also, both the MPEG-2 and VC-1 hwaccel decoders depend on this struct member,
but only the VC-1 decoder was disabled if the check failed.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

configure

@@ -1378,7 +1378,7 @@ truehd_decoder_select="mlp_decoder"
 tscc_decoder_select="zlib"
 twinvq_decoder_select="mdct lsp sinewin"
 vc1_decoder_select="h263_decoder h264chroma"
-vc1_dxva2_hwaccel_deps="dxva2api_h DXVA_PictureParameters_wDecodedPictureIndex"
+vc1_dxva2_hwaccel_deps="dxva2api_h"
 vc1_dxva2_hwaccel_select="dxva2 vc1_decoder"
 vc1_vaapi_hwaccel_select="vaapi vc1_decoder"
 vc1_vdpau_decoder_select="vdpau vc1_decoder"
@@ -2885,8 +2885,6 @@ check_header vdpau/vdpau.h
 check_header vdpau/vdpau_x11.h
 check_header X11/extensions/XvMClib.h
 
-check_struct dxva2api.h DXVA_PictureParameters wDecodedPictureIndex
-
 disabled  zlib || check_lib   zlib.h      zlibVersion -lz   || disable  zlib
 disabled bzlib || check_lib2 bzlib.h BZ2_bzlibVersion -lbz2 || disable bzlib