April 1 (Reuters) – A telecom tower unit of Singapore Telecommunications and pension fund AustralianSuper will buy rival Axicom, part-owned by investment bank giant Macquarie Group Ltd, for A$3.58 billion ($2.68 billion), the companies said on Friday. The purchase builds on SingTel’s physical footprint in Australia, where it already has No.2 telco provider Optus, while…