In some terminal, verified with gtkterm and teraterm, backspace key is
not properly processed. For instance, type 'abc', 3 times of backspace
key press then '123' shows the result of 'abc123' instead of '123'. To
fix this, add a routine to process '\b' character input when using
edit_simple.c instead of edit.c (i.e., without CONFIG_WPA_CLI_EDIT=y).
Signed-off-by: Siwon Kang <kkangshawn@gmail.com>