Debugger: remove platform ifdefs in terminal adapter

The code still assumes host == target in some places...

Change-Id: Ief495df6ff5fbff890fc46d42a6b29eee3a1ed2c
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Robert Loehning <robert.loehning@digia.com>