lavc/qsvenc_hevc: use open GOP by default

HEVC spec has CRA frame which allows random access with open GOP, hence
it can achieve higher compression efficiency.

Removing the entry was suggested by Andreas

Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>

libavcodec/qsvenc_hevc.c

@@ -294,7 +294,6 @@ static const FFCodecDefault qsv_enc_defaults[] = {
     { "qmin",      "-1"    },
     { "qmax",      "-1"    },
     { "trellis",   "-1"    },
-    { "flags",     "+cgop" },
     { NULL },
 };