Retire the argument `isic_tilt`, deprecated more than 8 weeks ago

[maurolepore]

We recently retired some deprecated code:

• Remove old API and the deprecation code #157

We may use the momentum and retire other stuff that was deprecated around the same time (more than 8 weeks ago).

https://github.com/search?q=repo%3A2DegreesInvesting%2FtiltIndicatorAfter%20deprecate_warn&type=code

cc @kalashsinghal