Remove all placeholder code in HildonEntry/TextView now that it's in GTK

Remove all placeholder code in HildonEntry/TextView now that it's in GTK

* hildon/hildon-text-view.c
* hildon/hildon-entry.c:
Remove all placeholder code from HildonEntry and HildonTextView
and use the API in GtkEntry and GtkTextView instead.

* examples/hildon-entry-example.c
* examples/hildon-text-view-example.c
* examples/hildon-wizard-dialog-example.c
* hildon/hildon-get-password-dialog.c
* hildon/hildon-login-dialog.c
* hildon/hildon-picker-dialog.c
* hildon/hildon-set-password-dialog.c
* hildon/hildon-touch-selector-entry.c:
Replace all deprecated calls to HildonEntry and HildonTextView
with their Gtk counterparts.

Fixes: NB#122395 (hildon_entry_set_placeholder() should be in
GtkEntry)