RCS and SCCS keywords

[Florian Weimer]

This is about markers such as:

static char sccsid[] = "@(#)inet_network.c 8.1 (Berkeley) 6/4/93";

Do we want to preserve these keywords?  Otherwise, I'd remove them if 
while I'm cleaning up other unused/always-used #defines.

Even if we remove them now, they are still available from the history. 
Their immediate benefit is unclear because I expect that many of these 
files have been edited before they were imported into glibc, so these 
markers do not indicate an unambiguous baseline of a file anyway.

Florian