configure: do not auto enable mlp decoder when enabling truehd decoder

It is generally bad idea even if codecs use same code.

Signed-off-by: Paul B Mahol <onemda@gmail.com>

configure

@@ -1535,7 +1535,6 @@ svq3_decoder_suggest="zlib"
 theora_decoder_select="vp3_decoder"
 tiff_decoder_suggest="zlib"
 tiff_encoder_suggest="zlib"
-truehd_decoder_select="mlp_decoder"
 tscc_decoder_select="zlib"
 twinvq_decoder_select="mdct lsp sinewin"
 vc1_crystalhd_decoder_select="crystalhd"