libmount: don't use setgroups at all()

It's probably good idea to call setgroups() to cleanup groups,
but it introduces a regression as some mount helpers depend on
supplementary groups like "network" etc.

Fixes: https://github.com/karelzak/util-linux/issues/1398
Signed-off-by: Karel Zak <kzak@redhat.com>

include/c.h

@@ -340,16 +340,10 @@ static inline size_t get_hostname_max(void)
 
 static inline int drop_permissions(void)
 {
-	gid_t newgid = getgid();
-
 	errno = 0;
 
-	/* drop supplementary groups */
-	if (geteuid() == 0 && setgroups(1, &newgid) != 0)
-		goto fail;
-
 	/* drop GID */
-	if (setgid(newgid) < 0)
+	if (setgid(getgid()) < 0)
 		goto fail;
 
 	/* drop UID */