Secrets cleanup

[justmobilize]

Minor updates to remove secrets usage and update keys:

1. Remove secrets_data
2. Update secrets.py comments to settings.toml
3. Update AIO keys from AIO_* to ADAFRUIT_AIO_*
4. Update learn links to point to correct page for settings.toml
5. Update adafruit_portalbase.network.NetworkBase._get_setting to handle newer ADAFRUIT_AIO_* key names and show a warning when using secrets (tests added to make sure it's working as expected)

Tested on a PyPortal running 9.2.4

[justmobilize]

@dhalbert I will make the ready for review after adafruit/Adafruit_CircuitPython_PyPortal#137 is merged and released (because of the secrets_data removal)

[dhalbert]

@justmobilize There are other libraries that use PortalBase: FunHouse, MagTag, ESP32S2TFT, Qualia, MatrixPortal (using the short names). I grep'd for PortalBase in the bundle to find all the mentions.

[justmobilize]

@dhalbert doing a search, PyPortal was the only one that used secrets_data: https://github.com/search?q=org%3Aadafruit%20secrets_data&type=code

[dhalbert]

@justmobilize 😄 ok, great!

[justmobilize]

Ahhh, didn't catch one. It's also used in the Adafruit_Blinka_PyPortal. Text truncation hid it from me. Will open that PR next.

[dhalbert]

I often search in a local clone of https://github.com/adafruit/Adafruit_CircuitPython_Bundle instead of using the GitHub search.

[justmobilize]

I did that originally. The blinka one isn't in there (since it's for CPythpn) and then when I sent you the GitHub search, I just saw PyPortal.

[justmobilize]

Issue opened adafruit/Adafruit_Blinka_PyPortal#23

[justmobilize]

@dhalbert this is ready for review

[dhalbert]

Looks good. I cleaned up the error messages a bit.