Remove icons

genjix@l:~$ cd /usr/share/awesome/lib/awful/widget/
genjix@l:/usr/share/awesome/lib/awful/widget$ sudo vim tasklist.lua 

Find the line (around line 123 in function called local function widget_tasklist_label_common(c, args)) like:

    text = text .. "</span>"
    -- return text, bg, status_image, c.icon
    return text, bg, status_image, nil
end

Commenting it with -- and changing the last c.icon to nil like above

If you prefer to configure as much as possible in the rc.lua do the following: find the command which creates the tasklist and let it look like this

	-- Create a tasklist widget
	mytasklist = awful.widget.tasklist(function(c)
		--remove tasklist-icon without modifying the original tasklist.lua
		local tmptask = { awful.widget.tasklist.label.currenttags(c, myscreen) }
		return tmptask[1], tmptask[2], tmptask[3], nil
	end, mytasklist.buttons)

this does basically the same thing as the changes in the tasklist.lua but later when the function returns content to the actual tasklist (be aware that the variable 'myscreen' refers to my configuration, i think originally you have this block in a for-loop and this 'myscreen' is an 'i')