Drop hardcoded LOCAL_C_INCLUDES from minui/Android.mk

The zlib include was not required. libpng is now handled by referencing
the libpng static library

Change-Id: Ie4e0abad3fff5b763eba363d3d0fa96128ff49bc
diff --git a/minui/Android.mk b/minui/Android.mk
index ddee165..9b2e09b 100644
--- a/minui/Android.mk
+++ b/minui/Android.mk
@@ -4,11 +4,8 @@
 LOCAL_SRC_FILES := graphics.c graphics_adf.c graphics_fbdev.c events.c \
 	resources.c
 
-LOCAL_C_INCLUDES +=\
-    external/libpng\
-    external/zlib
-
 LOCAL_WHOLE_STATIC_LIBRARIES += libadf
+LOCAL_STATIC_LIBRARIES += libpng
 
 LOCAL_MODULE := libminui