Remove unused index.html
Remove unused index.html

No code depends on it.

hifive/hifive-pitalium-explorer,hifive-snu/hifive-test-explorer,hifive/hifive-test-explorer,hifive-snu/hifive-test-explorer,hifive/hifive-pitalium-explorer,hifive/hifive-pitalium-explorer,hifive/hifive-pitalium-explorer,hifive/hifive-test-explorer,hifive-snu/hifive-test-explorer,hifive/hifive-test-explorer,hifive/hifive-test-explorer,hifive-snu/hifive-test-explorer