Inconsistently using plurals when defining multiple functions at once

[Halalaluyafail3]

Here is an example of this issue in atexit [support.start.term]:

Effects: The atexit() functions ...

And:

Returns: The atexit() function ...

In the effects it uses the plural to refer to both functions at once, but in the returns it uses the singular to refer to each function individually. Other places where this issue appears are all functions in [new.delete.single] and all functions in [new.delete.array]. There may be other instances of this issue, I only checked [support].

[jwakely]

We should remove the () from the Effects, and the Returns should just be "Zero if the registration succeeds, nonzero if it fails."