Just use --with-extra-buildid=Flatpak

...as suggested in comment <https://github.com/flathub/
org.libreoffice.LibreOffice/issues/48#issuecomment-399739393> to "LibreOffice
6.0.5": "Should 'Flatpak version' be just 'Flatpak' to save translation of
'version' in the string for non-English locales?"

Change-Id: I53171a5725f54520ae9e3cbaf294e291d16e1c78
Reviewed-on: https://gerrit.libreoffice.org/56390
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

distro-configs/LibreOfficeFlatpak.conf

@@ -2,7 +2,7 @@
 --disable-odk
 --enable-release-build
 --with-ant-home=/run/build/libreoffice/ant
---with-extra-buildid=Flatpak version
+--with-extra-buildid=Flatpak
 --with-jdk-home=/usr/lib/sdk/openjdk10/jvm/openjdk-10
 --with-lang=ALL
 --with-system-libs