Patch: drop NEC v810 support

[Jim Wilson]

It was a newlib only port, using the NEC compiler.  It was a rather unusual
port, and one that we don't need to worry about now.  Dropping the mt-v810
file is OK.

Dropping the port is OK too, but if we are doing that, then we may as well
delete the newlib bits.  The main part is in the lib/sys/sysnec810 directory
and the newlib configure.host file, but there are various files with 
#ifdef __v810__ in them to deal with NEC compiler specific issues.  Use
"find . -type f | xargs grep v810" to find them.  This isn't your problem
though, it is a problem for the newlib maintainers to worry about.

Jim