Remove replication of code to get_token command.

There are two separate blocks of code which perform the same task -

1. https://github.com/Cloud-CV/evalai-cli/blob/master/evalai/utils/auth.py#L53

2. https://github.com/Cloud-CV/evalai-cli/blob/master/evalai/get_token.py

Remove replication of code.

Compare the two referenced implementations in evalai/utils/auth.py around line 53 and evalai/get_token.py, starting with how the get_token command reaches each block. Consolidate the repeated task so only one implementation remains, while preserving the command's existing behavior. Done when the duplicate code is removed and get_token still works.

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