Code tidying - Remove unused variables, subroutines, dummy variables, etc.

[sbryngelson]

The CI runs on every PR a track of compiler warnings like unused dummy variables and such: https://github.com/MFlowCode/MFC/blob/master/.github/workflows/cleanliness.yml

and the output can be seen, e.g., here: https://github.com/MFlowCode/MFC/actions/runs/15242429158/job/42864167950

Warning: Unused variable ‘k_falloff’ declared at (1) [-Wunused-variable]
Warning: Unused PRIVATE module variable ‘col’ declared at (1) [-Wunused-value]
Warning: Unused PRIVATE module variable ‘tempname’ declared at (1) [-Wunused-value]
Warning: Unused variable ‘event’ declared at (1) [-Wunused-variable]
Warning: Unused dummy argument ‘id’ at (1) [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘name’ at (1) [-Wunused-dummy-argument]
Warning: Unused variable ‘k_falloff’ declared at (1) [-Wunused-variable]
Warning: Possible change of value in conversion from REAL([8](https://github.com/MFlowCode/MFC/actions/runs/15242429158/job/42864167950#step:11:9)) to INTEGER(4) at (1) [-Wconversion]
Warning: Unused dummy argument ‘fd_number_in’ at (1) [-Wunused-dummy-argument]
Warning: Possible change of value in conversion from COMPLEX(8) to REAL(8) at (1) [-Wconversion]
Warning: Unused PRIVATE module variable ‘err_code’ declared at (1) [-Wunused-value]
Warning: Unused dummy argument ‘mv’ at (1) [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘pb’ at (1) [-Wunused-dummy-argument]
Warning: Unused variable ‘q’ declared at (1) [-Wunused-variable]
Warning: Dummy argument ‘ccfl_max_glb’ at (1) was declared INTENT(OUT) but was not set [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘ccfl_max_loc’ at (1) [-Wunused-dummy-argument]
Warning: Dummy argument ‘icfl_max_glb’ at (1) was declared INTENT(OUT) but was not set [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘icfl_max_loc’ at (1) [-Wunused-dummy-argument]
Warning: Dummy argument ‘rc_min_glb’ at (1) was declared INTENT(OUT) but was not set [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘rc_min_loc’ at (1) [-Wunused-dummy-argument]
Warning: Dummy argument ‘vcfl_max_glb’ at (1) was declared INTENT(OUT) but was not set [-Wunused-dummy-argument]
Warning: Unused dummy argument ‘vcfl_max_loc’ at (1) [-Wunused-dummy-argument]
Warning: ‘p_send’ may be used uninitialized [-Wmaybe-uninitialized]
Warning: ‘p_recv’ may be used uninitialized [-Wmaybe-uninitialized]

This issue concerns removing unused variables, dummy variables, and other things that don't make sense in the code.

A warning to who works on this: Some of these will seem to persist because there are different compilation units, marked by #ifdef. For example

#ifdef MFC_PREPROCESS
...
#endif

others are MFC_SIMULATION, MFC_POSTPROCESS.

And some only happen if OpenACC GPU offloading is enabled (MFC_OPENACC) or MPI is enabled (MFC_MPI).

Most of these can be worked around by enclosing the offending variables with corresponding #ifdef and #endif tags

[sbryngelson]

Addressed via #1341