Remove $PRODUCT_OUT/vendor_kernel_ramdisk on installclean

Make sure the staging directory doesn't have stale file after
installclean.

Test: m installclean && ls $ANDROID_PRODUCT_OUT
Change-Id: Idcd7a883a6cba4b7eb1eb99751f5d03cba365a12
diff --git a/ui/build/cleanbuild.go b/ui/build/cleanbuild.go
index 1c80cff..fd60177 100644
--- a/ui/build/cleanbuild.go
+++ b/ui/build/cleanbuild.go
@@ -167,6 +167,7 @@
 		productOut("debug_ramdisk"),
 		productOut("vendor_ramdisk"),
 		productOut("vendor_debug_ramdisk"),
+		productOut("vendor_kernel_ramdisk"),
 		productOut("test_harness_ramdisk"),
 		productOut("recovery"),
 		productOut("root"),