Remove allowing `dict` arg to `connect()` and other backward compatible

From https://github.com/adafruit/Adafruit_CircuitPython_ESP32SPI/pull/199#issuecomment-2090654012:

- [x] Include the backwards compatible API (with appropriate documentation), so that old code will work. Merge and release this any time between now and just before 9.1.0 final.
- [x] Before releasing 9.1.0 final, update frozen libraries for 9.1.0 final with the upward compatible release. 9.1.0 will then work with the secrets dict and with the new API.
- [ ] After 9.1.0 final is released, we can change the Guide code to use the separate SSID and password arguments.
- [ ] Sometime after that, maybe 9.2 or 10.0, remove the backward compatibility.

Start by locating the connect() entry point and the Guide code that still uses the secrets dict, then review the backward-compatible API described in the issue. Confirm that 9.1.0 final has been released before removing the compatibility path; done means the separate SSID and password API is used and the old dict argument is no longer supported.

Written by the indexing model from the issue text.