MDEV-10180 main.events_restart fails on valgrind builder: void...

MDEV-10180 main.events_restart fails on valgrind builder: void THD::inc_thread_count(): Assertion `!abort_loop' failed.

remove an overly strong assert

sql/sql_class.h

@@ -1917,7 +1917,6 @@ class THD :public Statement,
   void inc_thread_count(void)
   {
     thread_safe_increment32(const_cast<int32*>(&thread_count));
-    DBUG_ASSERT(!abort_loop);
   }
 
 public: