config.h: remove unused git_config_get_untracked_cache() declaration

This function was removed in ad0fb65 (repo-settings: parse
core.untrackedCache, 2019-08-13), but not its corresponding *.h entry.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

config.h

@@ -606,7 +606,6 @@ int git_config_get_maybe_bool(const char *key, int *dest);
 int git_config_get_pathname(const char *key, const char **dest);
 
 int git_config_get_index_threads(int *dest);
-int git_config_get_untracked_cache(void);
 int git_config_get_split_index(void);
 int git_config_get_max_percent_split_change(void);
 int git_config_get_fsmonitor(void);