docs: Update example snippet (cosmetic)

[DaveSkender]

The guide was saying:

the get_history_from_feed() method shown in the example below and throughout our documentation is not part of this library

but then follows with a code snippet that used get_historical_quotes() inconsistently. I've updated them all to use the latter, since it's a bit nicer/simpler than "from feed".

[github-actions[bot]]

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