[uaxid.def.general] Replace non-codeblocks with outputblocks

These blocks are used for showing UAX syntax but not code, so presumably
`outputblock` should be used.

Co-authored-by: Eelis van der Weegen <eelis@eelis.net>

Author: frederick-vs-ja

source/uax31.tex

@@ -25,9 +25,9 @@
 \UAX{31} specifies a default syntax for identifiers
 based on properties from the Unicode Character Database, \UAX{44}.
 The general syntax is
-\begin{codeblock}
+\begin{outputblock}
 <Identifier> := <Start> <Continue>* (<Medial> <Continue>+)*
-\end{codeblock}
+\end{outputblock}
 where \tcode{<Start>} has the XID_Start property,
 \tcode{<Continue>} has the XID_Continue property, and
 \tcode{<Medial>} is a list of characters permitted between continue characters.
@@ -36,11 +36,11 @@
 the \tcode{<Medial>} set is empty, and
 the \tcode{<Continue>} characters are unmodified.
 In the grammar used in \UAX{31}, this is
-\begin{codeblock}
+\begin{outputblock}
 <Identifier> := <Start> <Continue>*
 <Start> := XID_Start + @\textrm{\ucode{005f}}@
 <Continue> := <Start> + XID_Continue
-\end{codeblock}
+\end{outputblock}
 
 \pnum
 This is described in the \Cpp{} grammar in \ref{lex.name},