Обсуждение: doc phrase: "inheritance child"

In this old sub-thread, we removed the use of word "partition" when it didn't
mean "declarative partitioning".

https://www.postgresql.org/message-id/flat/20180601213300.GT5164%40telsasoft.com#32efea8c1aa0e875d201873dac56e09c

Now, I'm proposing to get rid of the phrase "inheritance child" when it also
*does* apply to declarative partitioning.