mesa: Reset image unit state to the default values when a bound image is deleted.

mesa: Reset image unit state to the default values when a bound image is deleted.

The ES31-CTS.shader_image_load_store.basic-api-bind conformance test
expects the whole image unit state to be reset when the bound texture
object is deleted.  The ARB_shader_image_load_store extension is
rather vague regarding what should happen with image unit state other
than the texture object in that case, but the GL 4.2 and GLES 3.1
specifications (section "Automatic Unbinding of Deleted Objects")
explicitly require it to be reset to the default values.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>