flat_file cleaning to deal with winbuilder

[VincentGuyader]

there is no more out_dir anywhere in the package.

wy try to deal with this error :

* checking for missing documentation entries ... OK
* checking for code/documentation mismatches ... WARNING
Codoc mismatches from documentation object 'dock_from_renv':
dock_from_renv
  Code: function(lockfile = "renv.lock", distro = "focal", out_dir =
                 NULL, FROM = "rocker/r-base", repos = c(RSPM =
                 paste0("https://packagemanager.rstudio.com/all/__linux__/",
                 distro, "}/latest"), CRAN =
                 "https://cran.rstudio.com/"))
  Docs: function(lockfile = "renv.lock", distro = "focal", FROM =
                 "rocker/r-base", AS = NULL, sysreqs = TRUE, repos =
                 c(CRAN = "https://cran.rstudio.com/"), expand = FALSE,
                 extra_sysreqs = NULL)
  Argument names in code not in docs:
    out_dir
  Argument names in docs not in code:
    AS sysreqs expand extra_sysreqs
  Mismatches in argument names:
    Position: 3 Code: out_dir Docs: FROM
    Position: 4 Code: FROM Docs: AS
    Position: 5 Code: repos Docs: sysreqs
  Mismatches in argument default values:
    Name: 'repos'
    Code: c(RSPM = paste0("https://packagemanager.rstudio.com/all/__linux__/", 
          distro, "}/latest"), CRAN = "https://cran.rstudio.com/")
    Docs: c(CRAN = "https://cran.rstudio.com/")