F841 local variable is assigned but never used

[busunkim96]

tests/unit/texttospeech_v1beta1/test_text_to_speech.py:199:9: F841 local variable 'response' is assigned to but never used
tests/unit/texttospeech_v1beta1/test_text_to_speech.py:262:9: F841 local variable 'response' is assigned to but never used
tests/unit/texttospeech_v1beta1/test_text_to_speech.py:305:9: F841 local variable 'client' is assigned to but never used
tests/unit/texttospeech_v1/test_text_to_speech.py:154:9: F841 local variable 'client' is assigned to but never used
tests/unit/texttospeech_v1/test_text_to_speech.py:199:9: F841 local variable 'response' is assigned to but never used
tests/unit/texttospeech_v1/test_text_to_speech.py:262:9: F841 local variable 'response' is assigned to but never used
tests/unit/texttospeech_v1/test_text_to_speech.py:305:9: F841 local variable 'client' is assigned to but never used

googleapis/python-texttospeech#30

[miraleung]

@software-dov PTAL?

[software-dov]

Fixed by #428