Delete recommendations to mount fdescfs (freebsd#40)

fdescfs used to be useful to help Python more quickly close file
descriptors before exec().  But for years, Python has been using
closefrom() instead.  All versions of Python 3.9 and later do that.

Fixes freebsd#39

README.md

@@ -157,6 +157,3 @@ me:\
         net.link.bridge.pfil_onlyip=0  # Only pass IP packets when pfil is enabled
         net.link.bridge.pfil_bridge=0  # Packet filter on the bridge interface
         net.link.bridge.pfil_member=0  # Packet filter on the member interface
-- Lots of jails or a big server? Mount `fdescfs`:
-
-        mount -t fdescfs null /dev/fd

iocage_lib/ioc_check.py

@@ -54,7 +54,6 @@ def __init__(
         self.callback = callback
         self.silent = silent
 
-        self.__check_fd_mount__()
         self.__check_datasets__()
 
         self.pool_root_dataset = Dataset(self.pool, cache=reset_cache)
@@ -134,34 +133,3 @@ def __check_datasets__(self):
                 },
                     _callback=self.callback)
 
-    def __check_fd_mount__(self):
-        """
-        Checks if /dev/fd is mounted, and if not, give the user a
-        warning.
-        """
-
-        if os.path.ismount("/dev/fd"):
-            # all good!
-
-            return
-
-        messages = collections.OrderedDict([
-            ("1-NOTICE", "*" * 80),
-            ("2-WARNING", "fdescfs(5) is not mounted, performance"
-                          " may suffer. Please run:"),
-            ("3-INFO", "mount -t fdescfs null /dev/fd"),
-            ("4-WARNING", "You can also permanently mount it in"
-                          " /etc/fstab with the following entry:"),
-            ("5-INFO", "fdescfs /dev/fd  fdescfs  rw  0  0"),
-            ("6-NOTICE", f"{'*' * 80}\n")
-        ])
-
-        for level, msg in messages.items():
-            level = level.partition("-")[2]
-
-            iocage_lib.ioc_common.logit({
-                "level": level,
-                "message": msg
-            },
-                _callback=self.callback,
-                silent=self.silent)