Use shared lib of libtinyxml2 instead of static one.

libtinyxml2 is used commonly by vendors. So using its shared lib will reduce
total image size even though Android framework size increases as following for
now.

bluetooth.default.so: 1470356 -> 1440664 (-29692)
libtinyxml2.so      :       0 ->   46144 (+46144)
total               :                    (+16452)

Test: building succeeded, and the image was tested on angler.
Bug: 33056637
Change-Id: I3bd3cf7128e3ad6daa8157d57935f7422c1f2662