File open in micro_pumas_utils.F90 is not legal in CAM

There is a file open using unit 10 to read in lkuptable_filename. CAM can not guarantee that unit 10 won't already be open with some other file. See below for `newunit` which should be used

Obsolete comment - kept for documentation purposes, but should not be done._The unit number should be passed into the init_lookup_table subroutine and provided by the host model_.