Or in VI, just do:

  :%s/^V<Enter>//

that is, :s/  then Ctrl-V to accept a control
character, then the Enter key, and then two slashes.

This will remove all CR characters
throughout the file.

Obviously a command line is superior,
but this is good at the moment when you
VI a file and just want those ^Ms to go away.

I'm sure an equivalent is handy in Emacs.
(I also go to Emacs when VI chokes on
overlength lines.  Otherwise I stick with
VI largely because of its ubiquity.)

Vic