Replace ZoL with OpenZFS where applicable

Afterward, git grep ZoL matches:
  * README.md:  * [ZoL Site](https://zfsonlinux.org)
  - Correct
  * etc/default/zfs.in:# ZoL userland configuration.
  - Changing this would induce a needless upgrade-check,
    if the user has modified the configuration;
    this can be updated the next time the defaults change
  * module/zfs/dmu_send.c:   * ZoL < 0.7 does not handle [...]
  - Before 0.7 is ZoL, so fair enough

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Issue #11956

contrib/initramfs/hooks/zfs.in

@@ -1,9 +1,9 @@
 #!/bin/sh
 #
-# Add ZoL filesystem capabilities to an initrd, usually for a native ZFS root.
+# Add OpenZFS filesystem capabilities to an initrd, usually for a native ZFS root.
 #
 
-# This hook installs udev rules for ZoL.
+# This hook installs udev rules for OpenZFS.
 PREREQ="udev"
 
 # These prerequisites are provided by the zfsutils package. The zdb utility is

contrib/pyzfs/libzfs_core/test/test_libzfs_core.py

@@ -252,9 +252,9 @@ def skipUnlessBookmarksSupported(f):
 
 
 def snap_always_unmounted_before_destruction():
-    # Apparently ZoL automatically unmounts the snapshot
+    # Apparently OpenZFS automatically unmounts the snapshot
     # only if it is mounted at its default .zfs/snapshot
-    # mountpoint.
+    # mountpoint under Linux.
     return (
         platform.system() != 'Linux', 'snapshot is not auto-unmounted')