On POSIX systems, InnoDB would unconditionally acquire advisory locks
on the files that it opens. On Linux, this would be observable by
a large number of entries in /proc/locks.

Other storage engines would only acquire advisory locks on files
based on the Boolean configuration parameter external_locking.

Let InnoDB do the same.

NOTE: The --skip-external-locking is activated by default. To have
InnoDB acquire advisory locks, --external-locking must be specified.

Reviewed by: Sergei Golubchik