terminal-util: move lock_dev_console() here

It doesn't really make sense to have that in dev-setup.c, which is
mostly about setting up /dev/, creating device nodes and stuff.

let's move it to the other stuff that deals with /dev/console's
peculiarities.

src/shared/dev-setup.h

@@ -3,8 +3,6 @@
 
 #include <sys/types.h>
 
-int lock_dev_console(void);
-
 int dev_setup(const char *prefix, uid_t uid, gid_t gid);
 
 int make_inaccessible_nodes(const char *parent_dir, uid_t uid, gid_t gid);