[VOL-4308] Deprecating repo due to stale state

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+# DEPRECATED
+
+[![No Maintenance Intended](http://unmaintained.tech/badge.svg)](http://unmaintained.tech/)
+
+`VOLTHA 2.3` was the last official set of releases that  used the `voltha-ponsimonu-adapter` repository.
+From `2.4` onwards the [volta-openonu-adapter-go](https://github.com/opencord/voltha-openonu-adapter-go) as the exact same functionality in simulated or physical mode, thus the repo has been deprecated. This codebase is going to be removed after the VOLTHA 2.8 release LTS support ends in December 2022.