mp2: Do not force a samplerate

The default should be not to resample.
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  mp2: Do not force a samplerate

Conflicts:
	libavcodec/mpegaudioenc_template.c

Only libtwolame changes, as the forcing of a sample rate was not merged for the native mp2 encoder

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/dnxhdenc: use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>