xargs: use bb_ask_y_confirmation_FILE() instead of homegrown copy

xargs: use bb_ask_y_confirmation_FILE() instead of homegrown copy

function                                             old     new   delta
bb_ask_y_confirmation_FILE                             -      83     +83
inetd_main                                          2033    2043     +10
udhcp_send_kernel_packet                             295     301      +6
rmescapes                                            306     310      +4
send_tree                                            353     355      +2
i2cdetect_main                                       674     672      -2
confirm_or_abort                                      43      38      -5
get_terminal_width_height                            242     234      -8
bb_ask_y_confirmation                                 76      10     -66
xargs_main                                           823     755     -68
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/5 up/down: 105/-149)          Total: -44 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>