Deprecating Interfaces needs moving from wiki

Summary

This file:

• https://gitlab.rtems.org/rtems/docs/rtems-docs/-/blob/main/eng/coding-deprecating.rst?ref_type=heads

Needs to be populated by the contents of this file:

• https://gitlab.rtems.org/amar/old-wiki/-/blob/main/Developer/Coding/Deprecating.md?ref_type=heads

Needs to be done before %6.1 as part of devel.rtems.org decomissioning.

Steps to reproduce