Add "automatic-speech-recognition" to task_ids

LibriSpeech is a dataset for automatic speech recognition, see paper titled [LibriSpeech: An ASR Corpus Based On Public Domain Audio Books](https://www.danielpovey.com/files/2015_icassp_librispeech.pdf). This PR adds the ASR tag to the task ids in the yaml metadata and removes those for audio classification / speaker identification.

README.md

@@ -18,9 +18,8 @@ source_datasets:
 - original
 task_categories:
 - automatic-speech-recognition
-- audio-classification
 task_ids:
-- speaker-identification
+- automatic-speech-recognition
 ---
 
 # Dataset Card for librispeech_asr