[temp.{decls.general,dep.expr}] Editorial wording improvements

* Change definite to indefinite article.
* Drop unused name for a declaration.

Author: tkoeppe

source/templates.tex

@@ -2594,7 +2594,7 @@
 For the purpose of instantiation, the substatements of a constexpr if
 statement\iref{stmt.if} are considered definitions.
 For the purpose of name lookup and instantiation,
-the \grammarterm{compound-statement} of the \grammarterm{expansion-statement}
+the \grammarterm{compound-statement} of an \grammarterm{expansion-statement}
 is considered a template definition.
 
 \pnum
@@ -5668,7 +5668,7 @@
 \item
 a \grammarterm{conversion-function-id} that specifies a dependent type,
 \item
-a name $N$ introduced by the \grammarterm{for-range-declaration} $D$
+a name $N$ introduced by the \grammarterm{for-range-declaration}
 of an expansion statement $S$
 if the type specified for $N$ contains a placeholder type and either
 \begin{itemize}