Clean up Android.mk

Remove *.cl and *.java from LOCAL_SRC_FILES of native code. Neither is
used when compiling native code, and unused entries are being turned
into warnings to prevent typos.

Remove -L$(SYSROOT)/usr/lib from LOCAL_LDLIBS. SYSROOT is undefined in a
platform build, which means -L/usr/lib is added, which is very wrong.

Remove -lpng and -ljpeg from LOCAL_LDLIBS. LOCAL_LDLIBS should only be
used for components outside of the build system -- like libraries in the
NDK, or host libraries. Dependencies don't get set up properly if you
use LOCAL_LDLIBS with libraries that are being built.

Rename libjpeg module so that it isn't confused with external/jpeg.
Different modules are already using both in this file.

Remove $(LOCAL_PATH)/../zlib from LOCAL_C_INCLUDES. Since this is
linking against the libz from the NDK, it should be using the headers
from the NDK.

Remove $(LOCAL_C_INCLUDES:%=-I%) from LOCAL_CFLAGS. The build system
supports LOCAL_C_INCLUDES natively, the Android.mk does not have to do
anything.

Remove LOCAL_MODULE_TAGS := optional, which is the default.

Change-Id: I828d3facf9b2e17079cec0c5baadb05531d39a65