This reverts commit f9d996a460.
The change from calling glBindTexture to using the material API with
cogl_material_flush_gl_state does not always work because it doesn't
necessarily leave the active texture unit as GL_TEXTURE0. For example,
if the previously rendered texture was multi-layered then the last
thing cogl_material_flush_gl_state will do is select GL_TEXTURE1 just
to disable it.
c4dcbb6bdb