dissolve libcommon,libcommon-cs: clean up vty definitions

From openbsc.git, we still have osmo-msc's VTY definitions spread across
various places. Combine:

- Move the go_parent_cb() and is_config_node() to msc_main.c, drop
  common_vty.c.
- Move all of vty_interface_layer3.c into msc_vty.c.
- Move all of common_cs_vty.c into msc_vty.c.
- Move bsc_vty_init_extra() into msc_vty_init().
- Drop some unused definitions

No functional nor cosmetic changes have been made in the moved code, plain
copy-paste moving (even though the unidiff might look like edits in some
places). I might have adjusted some blank lines though.

Change-Id: Ia818c00ab613a19a34080b160d763b55c19f76b1
10 files changed