Remove strange `wordlen` variable in `mpp_do_redistribute.fh`

[foxtran]

Description During rewriting cray pointers in mpp/, I've noticed strange variable wordlen which is not used. So, here I've deleted it.

How Has This Been Tested? Compilation with GCC 15.2, CMake 4.1.1, NetCDF 4.9.3.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules
• [x] New check tests, if applicable, are included
• [ ] make distcheck passes