cpplib: cppexp.c final cleanup

[Neil Booth]

Zack Weinberg wrote:-

> Fine except for "putting the text #if between single quotes".  We are
> moving away from that convention.  Please take them back out again
> wherever you added them.  If you like, you may take them out in all
> the other messages in cppexp.c.  Then consider the patch approved.

OK, I've just removed them from #if.  For the other messages I've replaced
`' with '', and committed it.

Neil.