Things break without OpenSymbol font.  On the other hand, if you
install just the fonts, but not anything else, you can happily use
the fonts in other applications.  So just invert the dependency.

Change-Id: I4c2dbff59699365cba67d3b1c6ade5ec7c2462bf
Reviewed-on: https://gerrit.libreoffice.org/71898
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>