[pet] Remove additional @record in elastic_launch to fix file existing error
Summary:
Since `launch_agent()` in api.py is already decorated with record, we can remove the usage in elastic_launch.
It also fix the bug for FileExistError on MAST
We run an experiment to count how many times record is invoked in D27901961 to ensure the assumption.
Test Plan:
```
fbpkg build -E torchelastic_distributed_sum
buck run mode/dev-nosan //pytorch/elastic/torchelastic/tsm/fb/cli:tsm -- run_ddp --scheduler mast --fbpkg torchelastic_distributed_sum:fde7879 --nnodes 1 --nproc_per_node 1 --resource T1 --run_cfg hpcIdentity=oncall_dai_pet,hpcClusterUuid=MastNaoTestCluster main.par
```
https://www.internalfb.com/mast/job/tsm_wilsonhong-torchelastic_distributed_sum_a92f97e7
Reviewed By: borovsky-d
Differential Revision: D27902034
fbshipit-source-id: e08b02d4b9c7a7c70fbb0dbcb24b95af55d2ea95
