... and rename gimp_action_history_excluded_action() to
gimp_action_history_is_excluded_action().

is_blacklisted_action() determines whether an action should be
excluded from *both* the history and the search results, while
is_excluded_action() determines if an action should be excluded
only from the history.  This eliminates some redundancy across
gimpaction-history and action-search-dialog.