Revert "slaveactivity: forward isPeriodic() member call to the master…

… engine"

The mmaster pointer might be dangling and accessing it from the isPeriodic()
call in SlaveActivity::stop() triggers a segfault if the master is already
destroyed.

Ideally, activities would be managed in shared pointers only and the slave
activity uses the weak pointer concept to check if the master is still available.

This reverts commit cb4a376.

rtt/extras/SlaveActivity.cpp

@@ -178,8 +178,6 @@ namespace RTT {
 
     bool SlaveActivity::isPeriodic() const
     {
-        if (mmaster)
-            return mmaster->isPeriodic();
         return mperiod != 0.0;
     }
     bool SlaveActivity::isActive() const
@@ -204,7 +202,7 @@ namespace RTT {
     bool SlaveActivity::execute()
     {
         // non periodic case.
-        if ( !isPeriodic() ) {
+        if ( mperiod == 0.0 ) {
             if ( !active || running )
                 return false;
             running = true;