battery status: Remove battery-insecure-context.html. (web-platform-t…

…ests#32556)

This test does not reflect either the current spec or any implementation.

w3c/battery#30 removed the bits from the spec that mandated throwing a
SecurityError when the API was used in an insecure origin. Blink does not
perform any checks for a security context anyway, although the plan is to
switch spec and implementation to using [SecureContext] in the future, as
tracked in w3c/battery#15.