vi: some simplifications

function                                             old     new   delta
file_insert                                          301     315     +14
init_text_buffer                                     179     171      -8
colon                                               2889    2878     -11
file_size                                             37       -     -37
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/2 up/down: 14/-56)            Total: -42 bytes

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