Resolves: fdo#79172 dev builds were misleadingly labeled 'beta'

... but actual beta builds have no label. This commit GIMPs development
branding so that it reads 'development build' instead of 'beta'.

Change-Id: I5a7a7f480b97bec5afe54c366bf21e93e49b320b
Reviewed-on: https://gerrit.libreoffice.org/10313
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>