Mark libui as vendor_available

libui is used by libgui and libstagefright_foundation which are both in
VNDK. So libui should also be in VNDK.

Bug: 37731063
Test: sailfish builds and boots
Test: 'BOARD_VNDK_VERSION=current m libui' successful
Change-Id: Ia8172a42325e5b5181741dda70048dc68e778b76
Merged-In: Ia8172a42325e5b5181741dda70048dc68e778b76
diff --git a/libs/ui/Android.bp b/libs/ui/Android.bp
index b8ff207..395a98c 100644
--- a/libs/ui/Android.bp
+++ b/libs/ui/Android.bp
@@ -79,7 +79,6 @@
         "libsync",
         "libutils",
         "liblog",
-        "libgraphicsenv",
     ],
 
     static_libs: [