data: use a11y menu in initial-setup session

The a11yGreeter menu was removed in gnome-shell 3.27.1. It was identical
to the a11y menu, except that a11yGreeter was unconditionally visible,
whereas a11y hides itself unless a a11y tool is enabled or the
always-show-universal-access-status GSetting is true.

Using the correct name means the a11y menu will be shown if the distro
or administrator has overridden always-show-universal-access-status, but
is not enough to unconditionally show it.

GNOME/gnome-initial-setup#77
2 jobs for 77-a11y-menu in 3 minutes and 57 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #333585
build-maximal

00:03:56

passed #333584
build-minimal

00:03:57