gtk2 rbgtkscale.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgtkstock.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgtkfontbutton.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgtkentry.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgtkconst.c: drop GTK_CHECK_VERSION(2,4,0)