Just use `comphelper::OAccessibleTextHelper` directly
where `AccessibleTextHelper_BASE` is a typedef for that.
There are other `AccessibleTextHelper_BASE` typedefs with
a different meaning elsewhere in the codebase, which are left unchanged.
Change-Id: I323a2b103eccfcfc4f726caffa73e586decf6d65
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/163960
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
