configure: remove old libdcadec check

It's obsolete after the addition of the pkg-config check.
See http://comments.gmane.org/gmane.comp.video.ffmpeg.devel/191983 for the
relevant discussion
Reviewed-by: Hendrik Leppkes <h.leppkes@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -5016,8 +5016,7 @@ enabled libcelt           && require libcelt celt/celt.h celt_decode -lcelt0 &&
                              { check_lib celt/celt.h celt_decoder_create_custom -lcelt0 ||
                                die "ERROR: libcelt must be installed and version must be >= 0.11.0."; }
 enabled libcaca           && require_pkg_config caca caca.h caca_create_canvas
-enabled libdcadec         && { use_pkg_config dcadec libdcadec/dca_context.h dcadec_context_create ||
-                               { require libdcadec libdcadec/dca_context.h dcadec_context_create -ldcadec; }; }
+enabled libdcadec         && require_pkg_config dcadec libdcadec/dca_context.h dcadec_context_create
 enabled libfaac           && require2 libfaac "stdint.h faac.h" faacEncGetVersion -lfaac
 enabled libfdk_aac        && require libfdk_aac fdk-aac/aacenc_lib.h aacEncOpen -lfdk-aac
 flite_libs="-lflite_cmu_time_awb -lflite_cmu_us_awb -lflite_cmu_us_kal -lflite_cmu_us_kal16 -lflite_cmu_us_rms -lflite_cmu_us_slt -lflite_usenglish -lflite_cmulex -lflite"