[Development] always enable angle d3d11

[WangBin]

In fact d3d11 is dynamically loaded in ANGLE. It allows us to enable
d3d11 code when building. I have build with vs2013 and works fine on
windows xp (only d3d9 is loaded) and 8.1

In n libGLESv2.pro, remove

angle_d3d11: \
LIBS_PRIVATE += -ldxgi -ld3d11

and done

build for xp is a little complicate because dx headers in windows sdk
v7.1A miss something. i use win8.1 headers instead.