gui-apps/ReGreet: remove gtk4 useflasg

* can't be build with gtk3

Closes: https://bugs.gentoo.org/924751
Signed-off-by: Gonçalo Negrier Duarte <gonegrier.duarte@gmail.com>

gui-apps/ReGreet/ReGreet-9999.ebuild

@@ -25,14 +25,14 @@ RDEPEND="
 	|| ( gui-wm/sway gui-wm/cage )
 	systemd? ( sys-apps/systemd[sysv-utils] )
 	openrc? ( sys-apps/openrc[sysv-utils] )
-	gtk4? ( gui-libs/gtk ) || ( x11-libs/gtk+ )
+	gui-libs/gtk
 	gui-libs/greetd
 "
 BDEPEND="
 	virtual/rust
 	media-libs/graphene
 "
-IUSE="systemd openrc gtk4"
+IUSE="systemd openrc"
 
 src_configure() {
 	local myfeatures=(