cogl-material: Don't doubly ref the parent in cogl_material_copy
cogl-material: Don't doubly ref the parent in cogl_material_copy

cogl_material_copy was taking a reference on the original texture when
making a copy. However it then calls _cogl_material_set_parent on the
material which also takes a reference on the parent. The second
reference is cleaned up whenever _cogl_material_unparent is called and
this is also called by _cogl_material_free. However, it seems that
nothing was cleaning up the first reference. I think the reference is
entirely unnecessary so this patch removes it.

collects/cogl,collects/cogl,djdeath/cogl-android,djdeath/cogl,gcampax/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl-android,Distrotech/cogl,spatulasnout/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,spatulasnout/cogl,gcampax/cogl,Distrotech/cogl