gtkentryaccessible: Fix text-changed::delete length

The second parameter of the text-changed::delete event is to be the length,
not the end position.  This fixes spurious text removals in brltty
screen reading.
1 job for text-changed-delete in 7 minutes and 32 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build #21299

00:07:32