This method from the unpublished XAccessibleExtendedComponent
interface is not used by any of the a11y platform bridges, and
I don't know of any platform a11y API that would need it.

In order to report character/font attributes, there is the
XAccessibleText interface and its
XAccessiText::getCharacterAttributes method instead, which
actually gets used by the platform a11y bridges.

Therefore, drop this method to simplify code, and also decouple
the accessibility module a bit further from the toolkit
module without having to reorganize code further.
(VCLXFont from the toolkit module currently gets used in
various implementations.)

Change-Id: I06ea3cc5998a13927b3f869877b28f03ac07c89b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177809
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>