remove Thingspeak (unmaintained since 2015) (#3722)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/3558
- WARNING:awesome_lint.py: Thingspeak: last updated -2837 days, 4:04:51.290657 ago, older than 365 days
- ref. https://github.com/iobridge/thingspeak/issues

README.md

@@ -1126,7 +1126,6 @@ A [human resources management system](https://en.wikipedia.org/wiki/Human_resour
 - [OpenRemote](https://openremote.io) - Open-Source IoT Platform - IoT Asset management, Flow Rules and WHEN-THEN rules, Data visualization, Edge Gateway. ([Demo](https://demo.openremote.io/), [Source Code](https://github.com/openremote/openremote)) `AGPL-3.0` `Java`
 - [SIP Irrigation Control](https://dan-in-ca.github.io/SIP/) - Open source software for sprinkler/irrigation control. ([Source Code](https://github.com/Dan-in-CA/SIP)) `GPL-3.0` `Python`
 - [Thingsboard](https://thingsboard.io/) - Open-source IoT Platform - Device management, data collection, processing and visualization. ([Demo](https://demo.thingsboard.io/signup), [Source Code](https://github.com/thingsboard/thingsboard)) `Apache-2.0` `Java`
-- [Thingspeak](https://thingspeak.com/) - Open source “Internet of Things” application and API to store and retrieve data from things using HTTP. ([Demo](https://thingspeak.com/channels/public), [Source Code](https://github.com/iobridge/thingspeak)) `GPL-3.0` `Ruby`
 - [WebThings Gateway](https://webthings.io/gateway/) - WebThings is an open source implementation of the Web of Things, including the WebThings Gateway and the WebThings Framework. ([Source Code](https://github.com/WebThingsIO/gateway)) `MPL-2.0` `Nodejs`