I can verify that it still exists on Buster:
nils@smidge:/mnt/nas/backup/scripts/smidge$ mkdir tmp_locktest
nils@smidge:/mnt/nas/backup/scripts/smidge$ cd tmp_locktest/
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ lockfile-create
testlock
lockfile creation failed: Value too large for defined data type
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ ll
total 1
drwxr-xr-x 2 nils nils 0 Sep 6 09:56 ./
drwxr-xr-x 2 nils nils 0 Sep 6 09:55 ../
-rwxr-xr-x 2 nils nils 2 Sep 6 09:56 .lk01464asmidge*
-rwxr-xr-x 2 nils nils 2 Sep 6 09:56 testlock.lock*
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ lockfile-remove
testlock
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ ll
total 1
drwxr-xr-x 2 nils nils 0 Sep 6 09:57 ./
drwxr-xr-x 2 nils nils 0 Sep 6 09:55 ../
-rwxr-xr-x 1 nils nils 2 Sep 6 09:56 .lk01464asmidge*
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ uname -a
Linux smidge 5.10.0-0.bpo.5-686-pae #1 SMP Debian 5.10.24-1~bpo10+1
(2021-03-29) i686 GNU/Linux
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ cat
/etc/debian_version
10.10
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ dpkg -l | grep
libc6
ii libc6:i386
2.28-10 i386 GNU C Library:
Shared libraries
rc libc6-i686:i386
2.24-11+deb9u4 i386 transitional dummy
package
nils@smidge:/mnt/nas/backup/scripts/smidge/tmp_locktest$ dpkg -l | grep
liblockfile1
ii liblockfile1:i386
1.14-1.1 i386 NFS-safe locking
library
