Remove useless deployment scripts part

[4383]

python-varlink is now deployed on pypi through git tag creation and travis
triggering, so we can now remove some useless part of the deployment script.

[coveralls]

Pull Request Test Coverage Report for Build 250

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 15.526%

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Totals
Change from base Build 249:	0.0%
Covered Lines:	626
Relevant Lines:	4032

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💛 - Coveralls

[4383]

What do you think about using readthedoc instead of gh-pages?

It's possible to trigger doc updating from the github repo to readthedocs.io.

readthedoc will automatically retrieve the doc source and build and publish the new one from github without manual handling:

• https://docs.readthedocs.io/en/stable/connected-accounts.html