lib/util/charset: Remove 'display charset'

lib/util/charset: Remove 'display charset'

As discussed in 'CH_DISPLAY and gettext' on the samba-technical list:
http://lists.samba.org/archive/samba-technical/2011-June/078190.html

Setting this to a value other than 'unix charset' does not make sense,
as any system where the filesytem charset does not equal the terminal
charset will already have problems with programs as simple as 'ls'.
It also means that our output could not be pasted as our input in
interactive programs or onto our command line, as we never did
translate in the DISPLAY -> UNIX direction.

The d_printf() calls are retained in case we need to revisit this, and
to support display_set_stderr().

Andrew Bartlett