demo-dashboard-gateway-image: Include epiphany-app

This image doesn't need epiphany broweser per se, it actually needs the
epiphany browser for a specific app. Include epiphany-app and let the
epiphany dependency be pulled automatically.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

meta-ohos-demo/recipes-core/images/demo-dashboard-gateway-image.bb

@@ -4,10 +4,8 @@ SUMMARY = "Dashboard demo image: gateway"
 DESCRIPTION = "Home Assistant based image targeting a gateway device"
 LICENSE = "Apache-2.0"
 
-BROWSER ?= "epiphany"
-
 IMAGE_INSTALL_append = "\
-	${BROWSER} \
+	epiphany-app \
 	python3-appdaemon \
 	python3-homeassistant \
 	weston \