[intro.defs] Remove inappropriate paragraph.

Only specific, fixed wording is allowed in Clause 3.

Fixes ISO/CS 009 (C++23 DIS).

Author: tkoeppe

source/intro.tex

@@ -110,11 +110,6 @@
 \item IEC Electropedia: available at \url{https://www.electropedia.org/}
 \end{itemize}
 
-\pnum
-Terms that are used only in a small portion of this document
-are defined where they are used and italicized where they are
-defined.
-
 \indexdefn{access}%
 \definition{access}{defns.access}
 \defncontext{execution-time action}