[basic.def.odr] Remove duplicate "a"

Author: Andreas-Krug

source/basic.tex

@@ -406,7 +406,7 @@
 \item If $E$ is a class member access
 expression\iref{expr.ref} of the form
 $E_1$ \tcode{.} \opt{\keyword{template}} $E_2$,
-where $E_2$ designates a a non-static data member or
+where $E_2$ designates a non-static data member or
 a direct base class relationship,
 the set contains the potential results of $E_1$.
 \item If $E$ is a class member access expression