tests/fate/opus: change test to use the official reference samples

The official samples are 50% smaller
Avoid having reference samples which are strongly linked to the used resampler
implementation. (which for example would require new samples to be used if this
implementation changes)
Also its more correct to use the official samples instead of the current
decoder output

also enable tests
The tests also fully pass as well with the previous samples.

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