[stmt.pre] Remove stray cross-reference (#4959)

Author: JohelEGP

source/statements.tex

@@ -60,7 +60,7 @@
 a \grammarterm{statement} \tcode{S2} if
 \begin{itemize}
 \item
-  \tcode{S2} is a substatement of \tcode{S1}\iref{dcl.dcl},
+  \tcode{S2} is a substatement of \tcode{S1},
 \item
   \tcode{S1} is a \grammarterm{selection-statement} or
   \grammarterm{iteration-statement} and