[lex.pptoken] Turn non-normative text into a note

source/lex.tex

@@ -583,18 +583,16 @@
 Each preprocessing token that is converted to a token\iref{lex.token}
 shall have the lexical form of a keyword, an identifier, a literal,
 or an operator or punctuator.
-
-\pnum
 \indexgrammar{\idxgram{import-keyword}}%
 \indexgrammar{\idxgram{module-keyword}}%
 \indexgrammar{\idxgram{export-keyword}}%
+\begin{note}
 The \grammarterm{import-keyword} is produced
 by processing an \keyword{import} directive\iref{cpp.import},
 the \grammarterm{module-keyword} is produced
 by preprocessing a \keyword{module} directive\iref{cpp.module}, and
 the \grammarterm{export-keyword} is produced
 by preprocessing either of the previous two directives.
-\begin{note}
 None has any observable spelling.
 \end{note}