Remove log lines in llgs at launch time, add logging around PTY handling.

With these changes, remote llgs with $O now works properly:

$ lldb
(lldb) platform select remote-linux
(lldb) target create ~/some/inferior/exe
(lldb) gdb-remote {some-target}:{port}
(lldb) run

The sequence above will correctly redirect stdout/stderr over gdb-remote $O,
as is needed for remote debugging.  That sequence assumes there is a lldb-gdbserver
exe running on the target with {some-host}:{port}.

For local debugging with llgs, the following sequence also works, and
uses local PTYs instead to avoid $O and extra gdb-remote messages:

$ lldb
(lldb) settings set platform.plugin.linux.use-llgs true
(lldb) target create ~/some/inferior/exe
(lldb) run

The above will run the inferior using llgs on the local host, and
will use PTYs rather than $O redirection.
Remove unnecessary diffs from dev-llgs-local-launch vs. lldb TOT.