[diff.cpp20.utilities] Clean up codeblock after sentence for LWG3833.

Replaces "." with ";" in codeblock in wording, and terminate the
sentence before the codeblock with ":".

Author: burblebee

source/compatibility.tex

@@ -251,9 +251,9 @@
 
 \diffref{format.formatter.spec}
 \change
-Removed the \tcode{formatter} specialization
+Removed the \tcode{formatter} specialization:
 \begin{codeblock}
-template<size_t N> struct formatter<const charT[N], charT>.
+template<size_t N> struct formatter<const charT[N], charT>;
 \end{codeblock}
 \rationale
 The specialization is inconsistent with the design of \tcode{formatter},