Clean up the warning inside sanity():decimal.c in valgrind-max builds.

sql/my_decimal.h:
  HAVE_purify is defined in valgrind-max build as well: one possible 
  solution is to disable the sanity check in decimal.c in the valgrind-max
  build, but it's better to have more checks than less, for
  valgrind-max builds are not always used in conjunction with valgrind.

sql/my_decimal.h

@@ -85,7 +85,7 @@ class my_decimal :public decimal
   {
     len= DECIMAL_BUFF_LENGTH;
     buf= buffer;
-#if !defined(HAVE_purify) && !defined(DBUG_OFF)
+#if !defined(DBUG_OFF)
     /* Set buffer to 'random' value to find wrong buffer usage */
     for (uint i= 0; i < DECIMAL_BUFF_LENGTH; i++)
       buffer[i]= i;