Renaming of ERW-related variables

[tabeado]

Purpose of this PR

Adjustments in connection to REMIND-PR 2411

• Renaming of s33_co2_rem_pot to s33_rockRemPot
• Deletion of s33_costs_fix and renaming of vm_omcosts_cdr to vm_EW_transport_costs

Checklist:

I checked the tests when running buildLibrary and made sure that my changes

• do not create new complaints about summation checks.
• do not create new complaints about missing variables that are expected in the piamInterfaces package. (If needed, adjust piamInterfaces mappings based on the README.md. In case of complaints unrelated to your changes that you are unable to fix, please open an issue in piamInterfaces.)

[Copilot]

Pull request overview

This PR updates the Enhanced Weathering (EW) LCOE reporting to reflect the variable rename from s33_co2_rem_pot to s33_rockRemPot, while keeping backward compatibility by falling back to the old name when needed.

Changes:

• Replaced the EW removal-potential input read from GDX to prefer s33_rockRemPot and fall back to s33_co2_rem_pot.
• Updated the downstream EW-induced removal calculation to use the renamed variable.

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