fix(muscript): remove unsafe cast to string for any assign casted to string

muscript/src/main/java/io/gitlab/jfronny/muscript/ast/dynamic/assign/DynamicAssign.java

@@ -44,11 +44,6 @@ public class DynamicAssign extends DynamicExpr {
         return new BoolAssign(location, name, value.asBoolExpr());
     }
 
-    @Override
-    public StringExpr asStringExpr() {
-        return new StringAssign(location, name, value.asStringExpr());
-    }
-
     @Override
     public NumberExpr asNumberExpr() {
         return new NumberAssign(location, name, value.asNumberExpr());