hterm: change default terminal encoding to utf8
hterm: change default terminal encoding to utf8

Change the default terminal encoding to utf8.  Practically speaking,
this means graphics maps won't work by default.  Unicode aware progs
should be using UTF-8 anyways instead of changing the character map,
but it's not entirely clear how many still exist.  Lets find out!

BUG=chromium:747625

Change-Id: I593de701721293bbb85731d3e6b4c82cae989a2b
Reviewed-on: https://chromium-review.googlesource.com/591920
Reviewed-by: Brandon Gilmore <adbfbaf7e4f927b45ce8ad3e5043a632414a833b@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm