[3.12] Doc: Simplify the definition of 'soft deprecated' (GH-124988) (#125030)

(cherry picked from commit feca4cf64e9742b9c002d5533ced47e68b34a880)

Co-authored-by: Andrés Delfino <adelfino@gmail.com>
Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
Co-authored-by: Carol Willing <carolcode@willingconsulting.com>