[basic.def] Remove incorrect \grammarterm formatting for "declaration" (#8337)

Fixes NB US 12-026 (C++26 CD).

Author: eisenwave

source/basic.tex

@@ -188,7 +188,7 @@
 \pnum
 \indextext{declaration!function}%
 \indextext{definition}%
-Each entity declared by a \grammarterm{declaration} is
+Each entity declared by a declaration is
 also \defnx{defined}{define} by that declaration unless:
 \begin{itemize}
 \item