bug-fix for clipped_ppo not logging several signals + small cleanup

rl_coach/architectures/tensorflow_components/heads/head.py

@@ -61,8 +61,6 @@ class Head(object):
         self.regularizations = []
         self.loss_weight = tf.Variable([float(w) for w in force_list(loss_weight)],
                                        trainable=False, collections=[tf.GraphKeys.LOCAL_VARIABLES])
-        self.loss_weight_placeholder = tf.placeholder("float")
-        self.set_loss_weight = tf.assign(self.loss_weight, self.loss_weight_placeholder)
         self.target = []
         self.importance_weight = []
         self.input = []