frontend: Remove filterClusterConfig()
frontend: Remove filterClusterConfig()

This function was only used by the unit tests, but has little value
because DEFAULT_CLUSTER_CONFIG now only contains a few values, and those
will probably be removed in the future.

lander2k2/tectonic-installer,alexsomesan/tectonic-installer,squat/tectonic-installer,lander2k2/tectonic-installer,kyoto/tectonic-installer,alexsomesan/tectonic-installer,mrwacky42/tectonic-installer,squat/tectonic-installer,lander2k2/tectonic-installer,metral/tectonic-installer,metral/tectonic-installer,kyoto/tectonic-installer,mrwacky42/tectonic-installer,zbwright/tectonic-installer,alexsomesan/tectonic-installer,cpanato/tectonic-installer,kyoto/tectonic-installer,squat/tectonic-installer,cpanato/tectonic-installer,justaugustus/tectonic-installer,squat/tectonic-installer,lander2k2/tectonic-installer,hhoover/tectonic-installer,zbwright/tectonic-installer,metral/tectonic-installer,kalmog/tectonic-installer,metral/tectonic-installer,kyoto/tectonic-installer,justaugustus/tectonic-installer,zbwright/tectonic-installer,hhoover/tectonic-installer,justaugustus/tectonic-installer,zbwright/tectonic-installer,derekhiggins/installer,hhoover/tectonic-installer,hhoover/tectonic-installer,kalmog/tectonic-installer,metral/tectonic-installer,cpanato/tectonic-installer,justaugustus/tectonic-installer,mrwacky42/tectonic-installer,mrwacky42/tectonic-installer,kalmog/tectonic-installer,cpanato/tectonic-installer,zbwright/tectonic-installer,kyoto/tectonic-installer,mrwacky42/tectonic-installer,alexsomesan/tectonic-installer,derekhiggins/installer,hhoover/tectonic-installer,alexsomesan/tectonic-installer,justaugustus/tectonic-installer