doc: move ERR_FEATURE_UNAVAILABLE_ON_PLATFORM to current errors
ERR_FEATURE_UNAVAILABLE_ON_PLATFORM is incorrectly included in the list of errors that have never been released. It was added in 67e067eb and included in every release in the 14.x line.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines