`FHMAX_GFS_${cyc}` has no relevance in the global-workflow anymore

[aerorahul]

What new functionality do you need?

In past GFS implementations, the GFS forecast lengths varied between cycles; e.g. 00z and 06z forecasts would have been different lengths.
A search for FHMAX_GFS_ results in no hits beyond config.base and some places in the workflow generation.
They can be simplified to key on FHMAX_GFS
Running different forecast lengths for different cycles is no longer supported in the global-workflow.

What are the requirements for the new functionality?

Existing functionality and operation should not be impacted.

Acceptance Criteria

Requirements are met following the suggested changes in functionality.

Suggest a solution (optional)

Eliminate FHMAX_GFS_00 etc and consolidate around FHMAX_GFS.

[KateFriedman-NOAA]

Will also be updating FHMAX_GFS to be populated via yaml and user inputs instead of being hardcoded.