Remove the unused function prototype for connection_or_get_for_extend().
There is no function implementation.
Part of 33817.
void connection_or_clear_identity(or_connection_t *conn);
void connection_or_clear_identity_map(void);
void clear_broken_connection_map(int disable);
-or_connection_t *connection_or_get_for_extend(const char *digest,
- const tor_addr_t *target_addr,
- const char **msg_out,
- int *launch_out);
void connection_or_block_renegotiation(or_connection_t *conn);
int connection_or_reached_eof(or_connection_t *conn);