[toplevel] Remove unused libc_interface stuff

[Jim Wilson]

Nathanael Nerode wrote:
> 	* config.if: Remove unused libc_interface determination.

I wrote roughly the same patch a couple of days before to fix GCC PR 
2236, but hadn't gotten around to testing it with a bootstrap.  I'll 
close GCC PR 2236 now. 
http://gcc.gnu.org/ml/gcc-patches/2003-07/msg01034.html

I also noticed that the comments for libstdcxx_incdir are wrong.  This 
used to be libstdcxx_interface, which was an interface name for 
libstdc++.  It was later changed to be libstdcxx_incdir which holds a 
version number for the libstdc++ header files, but the comment at the 
top of the file still claims that it is an interface name.  It isn't.

Also, since we no longer use the file to define any InferFace (IF) 
names, it seems kind of silly to keep it around.  It probably should be 
folded into other files and eliminated.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com