Eliminate TG_Buf_Utf8 global
Eliminate TG_Buf_Utf8 global

The TG_Buf_Utf8 was a temporary buffer used for UTF-8 conversions, when
the internal string format of Rebol was either Latin1 or UCS2.  After
UTF-8 Everywhere, the mold buffer sufficed as the one global buffer
for temporarily building UTF-8 strings.

giuliolunati/ren-c,giuliolunati/ren-c,giuliolunati/ren-c,giuliolunati/ren-c,giuliolunati/ren-c