Mark file-local symbols as "static", and drop functions that nobody
uses.
* jc/unused-symbols:
shallow.c: make check_shallow_file_for_update() static
remote.c: make clear_cas_option() static
urlmatch.c: make match_urls() static
revision.c: make save_parents() and free_saved_parents() static
line-log.c: make line_log_data_init() static
pack-bitmap.c: make pack_bitmap_filename() static
prompt.c: remove git_getpass() nobody uses
http.c: make finish_active_slot() and handle_curl_result() static