[lex.token] Strike mention of whitespace in phase 7

[AlisdairM]

It is meaningless to talk of whitespace separating tokens in phase 7 as whitespace is discarded at the end of phase 4.

[eisenwave]

I'm not convinced we should totally remove this wording without even leaving a note. It's a helpful insight that whitespace acts as a separator between the tokens that are processed in this subclause (even if the process of separation happens in a much earlier phase).

Perhaps we could keep just the note that is deleted in this PR and explicitly point out in which phase that separation takes place, with an \iref{lex.phases}.

[AlisdairM]

I was requested several times in review of other changes to remove this text. It has no normative impact, and truly is nonesense as whitespace does not separate tokens, it simply does not exist for several phases of translation before tokens even exist.

We have already improved the text around phases 3 and 4 where we state that whitespace separates preprocessing tokens, and there are no parts of this text that seem useful to transfer to those other notes.