cleanup: remove dead code, fix bugs, refactor SSH dest parsing

- Remove debug printf calls from file.c
- Remove dead code: chunk_print, chunk_format, chunk_data_create/delete
- Remove unused config.use_single_send_per_file field
- Fix server_delete() no-op (double-pointer)
- Fix double cast (long)(long) -> ptrdiff_t in chunk.c
- Fix thread return value: thrd_error instead of 1
- Remove unused config param from receive_chunk_enqueue()
- Make queue_double_capacity() static
- Move SSH dest parsing into config.c as config_parse_ssh_dest()
- Fix test_config_ssh_dest to test parsing round-trip
- Remove chunk_format test (obsolete format)
- Replace chunk_data_delete with data_destroy in tests

src/shared/file.h

@@ -22,7 +22,6 @@ typedef struct {
 File *file_create(const char *path);
 void file_destroy(void *item);
 void file_load_data(File *file);
-void file_print(void *item);
 void file_send_single_calls(File *file, int file_descriptor, bool use_metadata);
 void file_send_sendfile(File *file, int file_descriptor, bool use_metadata);
 size_t file_content_to_buffer(File *file);