remove non-working link to API docs
remove non-working link to API docs

All documentation is now included in the main documentation site, there
is no separate API documentation anymore.

Sign2Pay/magento-sign2pay,magently/magento-sign2pay,Sign2Pay/magento-sign2pay,Sign2Pay/magento-sign2pay,magently/magento-sign2pay,magently/magento-sign2pay