ngcgui: bug fixes for gcmc usage

1) decline gcmc file if not in linuxcnc path
2) if not embedded and gcmc file, use file dir as outdir with message
3) remove leftover id of gcmc file when not found
ngcgui: remove deprecated globals entry boxes

This was never a good idea, was undocumented, and noted as
deprecated in docs/src/gui/ngcgui.txt.

The plentiful availability of global-named-readonly-parameters
in the master branch makes support even more problematic