tests: Remove default value vars from metal.tfvars.json
tests: Remove default value vars from metal.tfvars.json

These smoke test input vars were set to their default value, so don't
need to be included. Excluding these default values matches the
behaviour of the GUI.

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