Gnc-Prefs: remove toolbar_style preference

This option should be handled by the environment, not by GnuCash

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23246 57a11ea4-9604-0410-9ed3-97b8803252fd
Gnc-Prefs: migrate GtkRadiobutton widgets (and associated preferences)

All GtkRadiokButtons now use the new preferences backend
so drop the GtkRadiokButton-Gconf wiring as well.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23247 57a11ea4-9604-0410-9ed3-97b8803252fd