Re: compilation-forget-errors still used by tex-mode.el

[Richard Stallman]

    To tell you the truth, I don't know what compilation-forget-errors is
    supposed to do.  In the old code it was supposed to erase previous parsing
    info and force a reparse at the next C-x `, but that's a very operational
    description whereas we need a more denotational description here if we want
    to make a useful version for the new code.

Perhaps there is no longer any role for compilation-forget-errors
in the new scheme.

The usual way to call compilation-forget-errors was by doing C-u C-x `.
I did that after deleting some of the lines which contained errors,
to remove the corresponding markers from the list of errors.
One of the advantages of the new code is that there's no need
to do anything special in that case--it will simply work.

I think we can simply make it a no-op.