fix: cleanup failed agent creation

[cpacker]

Close #709

Please describe the purpose of this pull request.

From Discord:

When running memgpt run --preset foo-system --persona foo --agent foo --human bar for the first time, if the setup fails (in my case because i hadn't deployed the preset files yet), the new agent dir and config is created, but not the state file.
When I run it again, startup fails due to a missing agent state file.
Deleting the agent dir allows the agent to be created successfully

Reproducing the error:

memgpt run --preset banana

? Would you like to select an existing agent? No

🧬 Creating new agent...
->  🤖 Using persona profile 'sam_pov'
->  🧑 Using human profile 'basic'
Failed to create agent from provided information:
Preset 'banana.yaml' not found

$ ls -lrt ~/.memgpt/agents
agent_1
agent_2

$ ls -lrt ~/.memgpt/agents/agent_2
config.json

How to test

Run memgpt run --preset banana and make sure no new directory is created (ie it's created, then deleted).

Have you tested this PR?

Yes:

% ls -rt ~/.memgpt/agents
agent_1

% memgpt run --preset banana

? Would you like to select an existing agent? No

🧬 Creating new agent...
->  🤖 Using persona profile 'sam_pov'
->  🧑 Using human profile 'basic'
Failed to create agent from provided information:
Preset 'banana.yaml' not found

% ls -rt ~/.memgpt/agents   
agent_1

[cpacker]

@sarahwooders not sure if this is too dangerous (rm -r) - alternatively we could move to /tmp instead of deleting?