vi: nuke FEATURE_VI_OPTIMIZE_CURSOR

vi: nuke FEATURE_VI_OPTIMIZE_CURSOR

It is not Unicode safe, it is not saving much of I/O, and it's large:

function                                             old     new   delta
vi_main                                              255     253      -2
go_bottom_and_clear_to_eol                            28      26      -2
do_cmd                                              4194    4182     -12
show_status_line                                     388     374     -14
strncat                                               39       -     -39
__GI_strncat                                          39       -     -39
refresh                                              774     724     -50
place_cursor                                         276      83    -193
------------------------------------------------------------------------------
(add/remove: 0/3 grow/shrink: 0/6 up/down: 0/-351)           Total: -351 bytes

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