[basic.fundamental] Remove "integer type"

[eisenwave]

We currently have https://eel.is/c++draft/basic.fundamental#11.sentence-3:

A synonym for integral type is integer type.

This synonym is negatively useful; it is confusing and adds no value. We arbitrarily use "integer type" and "integral type" in different places.

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3701r0.html#wording contains a superset of the necessary changes. We can get rid of this definition and replace "integer" with "integral" where appropriate. I'm not sure if P3701R0 could find consensus though; irrespective of that, the editorial change makes sense.

@jensmaurer has expressed some appetite for such a change in the past.

See

• P3701 R0 Concepts for integer types, not integral types papers#2330 (comment)