This is done by using standard joomla pagination code not FLEXIcontent code, i am not sure if it is editable the way you describe without hacking joomla core files.
So the simple would be to use css to hide them, something like (for joomla v1.6/v1.7):
#flexicontent .pagination-start,
#flexicontent .pagination-end,
#flexicontent .pagination-prev,
#flexicontent .pagination-next {
display:none;
}
for J1.5 there are no css classes,
you best chance would be to use str_replace or preg_replace on the $this->pageNav string inside the
components/com_flexicontent/category/tmpl/default.php
NOTE: BETTER CREATE a joomla template override
Code:
$this->pageNav = str_replace('/<span>Start</span>/', '', $this->pageNav);
But you will need to create a replacement for every language