Looks like idlc ignores the lone (due to the preceeding ";") raises
specification, for whatever buggy reason.  XAxis.idl had been like this since
the inception, and the C++ implementation of getAxisGroup in
sc/source/ui/vba/vbaaxis.{cxx,hxx} had also failed to list BasicErrorException
since its inception (likely because the function signatures were copied directly
from the generated .hdl file, which of course also lacks BasicErrorException;
and also does not really need it given the function definition just returns a
member variable), so keep the status quo and clean up the .idl file.

Change-Id: Ib4ffddb6ec867ca302cc595915cae17099734ddf