Disable `selected_pafy_pls_id` (soft revert: d69a959)

[gdbiles]

Fixes: https://github.com/iamtalhaasghar/yewtube/issues/75

Reverted commit intends to enable full playlist download (non-paginated). The change introduces bug when view does not set g.selected_pafy_pls_id prior to save.

This functionality was already available via dump command:

dump - to show entire contents of an opened YouTube playlist.
             (useful for playing or saving entire playlists, use undump to     undo)

Testing:

$ tail -n 5 ~/.config/mps-youtube/input_history
pl UUOkFff6Mg5YEyeZ8XONGc9A
save test_pl_nodump
dump
save test_pl_withdump
ls
      19  test_pl_nodump      36      38:30:36
      20  test_pl_withdump    177     130:33:26