Non-macro.
edit|replace
what: (hit and hold the alt key and type 0010 from the numeric keypad)
with: (leave blank or a spacebar???)
replace all
It may not look like that alt-0010 did anything, but try it. It'll work.
As a formula:
=substitute(a1,char(10),"")
or
=substitute(a1,char(10)," ")
If you want a space character.