Remove unused 'add_memory' method on the agent to simplify the API. T…

…he correct approach to adding a memory is to call 'observe'. For this to work, you have to make sure there is a component like observation that writes observations to memory. If you want to configure the importance, as was possible with 'add_memory', then you can also accomplish that through the memory writing component.

PiperOrigin-RevId: 636301686
Change-Id: I3fdd6dab637de2a014f851bccf1dc752ca0035fb

concordia/agents/basic_agent.py

@@ -287,9 +287,6 @@ def get_externality(externality):
 
     return output
 
-  def add_memory(self, memory: str, importance: float | None = None):
-    self._memory.add(memory, importance=importance)
-
   def say(self, conversation: str) -> str:
     convo_context = (
         f'{self._agent_name} is in the following'