Remove icons from bitmap directory.
The buttons are being removed because the bmp and png files are binary
and binary files cannot be included in a vimball. For users that are
starting to use Vim on Windows and who don't known very well how files
are organized in the Windows file system, it's easier to install a
vimball than to unpack the zip file and, then, run :helptags in the
correct directories. Moreover, the buttons are more a cosmetic than a
practical addition because Vim users are expected to use the keyboard
and not the mouse. Anyway, people who want to add the buttons can
download them from http://www.lepem.ufc.br/jaa/bitmaps.zip