Docs: Remove "private" designation from `_doing_it_wrong()` and related functions:

* `_deprecated_function()`
* `_deprecated_argument()`
* `_deprecated_constructor()`
* `_deprecated_file()`

Plugins and themes should be allowed to use these functions to throw appropriate error notices.

This brings them in line with newer `do_action_deprecated()` and `apply_filters_deprecated()` functions, which are not marked as private.

Props jrf.
Fixes #48251.
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git-svn-id: https://core.svn.wordpress.org/trunk@46399 1a063a9b-81f0-0310-95a4-ce76da25c4cd