Remove deprecated batch stock request AlphaVantage API service function.

Problem/Motivation

The AlphaVantage stock API removed support for batch stock data requests. The correlated API function in stocks_api, batchRequestStockQuotes(), should also be removed.

Steps to reproduce

If you try using the batchRequestStockQuotes() function in AlphaVantageStockAPI, no valid HTTP response is received, due to removal of the API URL endpoint on the AlphaVantage side.

Proposed resolution

Remove API functions marked as 'deprecated', including batchRequestStockQuotes().

Remaining tasks

Remove batchRequestStockQuotes() API function in 3.0 release.

User interface changes

None.

API changes

Remove batchRequestStockQuotes() function.

Data model changes

None.