Removing a duplicate use statement of FMS function "write_version_number"

[laurenchilutti]

Description

The FMS 2021.02-beta1 testing tag code requires the write_version_number subroutine be loaded from fms_mod. Any use of write_version_number from fms_io_mod will now give a compilation error. tools/fv_diagnostics.F90 has loaded this subroutine via both fms_io_mod and fms_mod. This PR removes the fms_io_mod write_version_number use statement

Fixes # (issue)

How Has This Been Tested?

I have verified this works when testing for PR #74. I have also verified that the code compiles with FMS tag 2021.02-beta1.

Checklist:

Please check all whether they apply or not

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules