Remove check for a failed googleapiclient upgrade

[epall]

oauth2client is not even a required dependency now, so this check throws a confusing error message

This sort of fixes #521, but I still can't import apiclient.discovery without having oauth2client installed:

>>> from apiclient import discovery
Traceback (most recent call last):
  File "/Users/epall/projects/google-api-python-client/googleapiclient/sample_tools.py", line 32, in <module>
    from oauth2client import client
ModuleNotFoundError: No module named 'oauth2client'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/epall/projects/google-api-python-client/apiclient/__init__.py", line 13, in <module>
    from googleapiclient import sample_tools
  File "/Users/epall/projects/google-api-python-client/googleapiclient/sample_tools.py", line 36, in <module>
    raise ImportError('googleapiclient.sample_tools requires oauth2client. Please install oauth2client and try again.')
ImportError: googleapiclient.sample_tools requires oauth2client. Please install oauth2client and try again.
>>>

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[epall]

I signed the CLA!

[googlebot]

CLAs look good, thanks!

[atc0m]

Please merge this as soon as possible! Thank you!

[theacodes]

Thanks, @epall!