Creating a GraphicObject with the uniqueID isn't supported anymore,
so exposing the uniqueID doesn't make much sense. Both are removed
from the API with this commit. Code paths that used it were
refactored to use the alternative (property which transports
XGraphic or XBitmap).

XGraphicObject can now only be created empty and the XGraphic can
be set to it with setGraphic property.

Change-Id: I4df5ce0aef8814d482482effdbb4521a84252360
Reviewed-on: https://gerrit.libreoffice.org/53242Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>