Change the is_del() macro to not regard ATTR_BOLD nor ATTR_RESET as delimiters.
Remove old iffed-out version of is_del() as well, as a cleanup step; that change
was for not regarding left and right parens as delimiters.  With this change,
mousing over a nickname will underline it even if it contains embedded formatting
data; it used to work with all formatting data but bold and reset; now it
works for all.