Remove api_connection() method from Salesforce source

[mgardzinski]

Comment from @trymzet:
This function should just be part of to_df(), or at least renamed to to_records() if you want to have an intermediate representation. If you want to do that then pls also add proper return type. Also, there's no need to keep data as an attribute (self.data) - just return it directly in to_df() or to_records() (if you wish to keep this one). Eg.

Suggested change:

def to_records(self, ...) -> list[dict[str, Any]]:
    ...
   return records

def to_df(self, ...) -> pd.DataFrame:
    records = self.to_records(...)
    df = pd.DataFrame(records)
    ...