Require unsized half-float textures to be renderable

Require unsized half-float textures to be renderable

The GL_EXT_color_buffer_half_float spec is pretty clear on requiring
this:

    If OES_texture_half_float is supported, textures created with:

	<internalformat> = RGBA
	<format> = RGBA
	<type> = HALF_FLOAT_OES

    are renderable.

Affects:
  dEQP-GLES2.functional.fbo.completeness.renderable.texture.color0.rgba_half_float_oes