[class.access] Replace "ncbnftab" environment with "ncsimplebnf" where no actual tabbing is used.

Author: zygoloid

source/access.tex

@@ -194,9 +194,9 @@
 \grammarterm{access-specifier}
 (\ref{class.derived}):
 
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 access-specifier \terminal{:} \opt{member-specification}
-\end{ncbnftab}
+\end{ncsimplebnf}
 
 An
 \grammarterm{access-specifier}