[array.cons] Fix various wording issues

[Eisenwave]

This PR fixes the following issues:

• "The conditions for an aggregate shall be met." does not specify that array meets those requirements, and usually we say this explicitly instead of letting the reader figure it out based on the subclause the wording is in. If we reworded this sentence to say "An array is an aggregate" (or something similar), this would just be repeating [array.overview] p2, and we don't need the same normative wording copied and pasted multiple times. Therefore, the first sentence is deleted.

• "Class array" is wrong. array is a class template, not a class. In the rest of [array], we say "an array" which is not wrong at least; it can be seen as a shorthand for "a specialization of the array class template".

• "implicit move constructor" is wrong. It's not a defined term, and could reasonably be interpreted to mean "the non-explicit move constructor", i.e. converting constructor. That's not what we are trying to say here; we are talking about the implicitly-declared move constructor.

I believe the LWG intent is clear enough for all of these issues to be editorial.

[jwakely]

Seems like an improvement, and doesn't conflict with https://cplusplus.github.io/LWG/issue4069

[jensmaurer]

Looks fine.