hterm: character maps: mark internal variables with _ suffixes
hterm: character maps: mark internal variables with _ suffixes

We don't really expect people to access these maps directly, so mark
them all as internal.  The only real exported API are the GL/GR funcs.

BUG=chromium:734318

Change-Id: I7cd000be86f4c97609176c2498ff0345c44c1a98
Reviewed-on: https://chromium-review.googlesource.com/539175
Reviewed-by: Brandon Gilmore <adbfbaf7e4f927b45ce8ad3e5043a632414a833b@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

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