bob.io.matlab is deprecated

bob.io.matlab usage needs to be dropped here. see bob.io.matlab#5 (closed)

bob.io.audio/requirements.txt
7:bob.io.matlab

bob.io.audio/bob/io/audio/test.py
14:import bob.io.matlab

bob.io.audio/develop.cfg
15:          src/bob.io.matlab
28:bob.io.matlab = git https://gitlab.idiap.ch/bob/bob.io.matlab

bob.io.audio/conda/meta.yaml
32:    - bob.io.matlab