The use of its progname is justified by klibc support. Support for klibc
has been removed for a very long time. We support and test only glibc
and musl which have support of program_invocation_short_name.
Since vlock already uses _GNU_SOURCE, it seems reasonable to stop using
its progname and use program_invocation_short_name everywhere.
Signed-off-by: Alexey Gladkov <legion@kernel.org>