utf8.c: Stop using two functions

utf8.c: Stop using two functions

This is in preparation for deprecating these functions, to force any
code that has been using these functions to change.
Since the Unicode tables are now stored in native order, these
functions should only rarely be needed.

However, the functionality of these is needed, and in actuality, on
ASCII platforms, the native functions are #defined to these.  So what
this commit does is rename the functions to something else, and create
wrappers with the old names, so that anyone using them will get the
deprecation when it actually goes into effect: we are waiting for CPAN
files distributed with the core to change before doing the deprecation.

According to cpan.grep.me, this should affect fewer than 10 additional
CPAN distributions.