inference: check if file exist before deleting it (for log sanity)

[jcblemai]

After an inference interation, filter_MC removes unused files, but in most cases these files do not exist which results in warning such as

Warning: Removing unused files
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/seed/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.seed.csv', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/seir/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.seir.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/snpi/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.snpi.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/hnpi/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.hnpi.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/spar/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.spar.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/hosp/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.hosp.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/hpar/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.hpar.parquet', à cause de 'No such file or directory'
Warning in FUN(X[[i]], ...) :
  impossible d'effacer le fichier 'model_output/llik/KOR/inference/med/2023.02.13.23:43:06.CET/global/intermediate/000000001.000000001.000000000.2023.02.13.23:43:06.CET.llik.parquet', à cause de 'No such file or directory'

which pollute log. Filter_MC should check before deleting.