Clarify that mixin application drops static members

Change-Id: If0adcdb9423d856d629dd8002ba843697dafb770
Reviewed-on: https://dart-review.googlesource.com/49360
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>

docs/language/dartLangSpec.tex

@@ -2593,7 +2593,8 @@ A mixin application of the form \code{$S$ \WITH{} $M_1,\ \ldots, M_k$;} for the
 \rationale{The name of the resulting class is necessary because it is part of the names of the introduced constructors.}
 
 \LMHash{}
-In both cases above, $C$ declares the same instance members as $M$ (respectively, $M_k$).
+In both cases above, $C$ declares the same instance members as $M$ (respectively, $M_k$),
+and it does not declare any static members.
 If any of the instance variables of $M$ (respectively, $M_k$) have initializers,
 they are executed in the instance scope of $M$ (respectively, $M_k$)
 to initialize the corresponding instance variables of $C$.