By Michael Holden LONDON (Reuters) -Queen Elizabeth plans to attend major celebrations to mark her 70 years on the British throne next month, Buckingham Palace said on Friday, but two out-of-favour royals, Princes Andrew and Harry, will be excluded from one traditional event. The 96-year-old, Britain’s longest-reigning monarch, marked seven decades as queen in February, and four days of “Platinum Jubilee” events to recognise that landmark are being held at the start of June. Elizabeth has been struggling with mobility issues, meaning most of her recent public engagements have had to be cancell…