By Tom Balmforth and Olena Harmash KYIV (Reuters) -Security services searched the home of one of Ukraine’s most prominent billionaires on Wednesday, moving against a figure once seen as President Volodymyr Zelenskiy’s sponsor in what the authorities called a war-time anti-corruption purge. The action, days before a summit with the European Union, appears to reflect determination by Kyiv to demonstrate that it can be a steward of billions of dollars in Western aid and shed a reputation as one of the world’s most corrupt states. It came as Kyiv has secured huge pledges of weapons from the West i…