June 23 (Bloomberg) — Google Inc.\u2019s reluctance to provide a top executive for testimony to a Senate panel probing its market power has prompted threats of subpoenas for Chief Executive Officer Larry Page and Chairman Eric Schmidt.   The Democratic chairman and leading Republican on the antitrust subcommittee asked Google to provide one of the company\u2019s two senior executives before Congress\u2019s August recess, according to a copy of a June 10 letter obtained by Bloomberg News. Sara Forden reports on…