Fix Mitochondrial Glutathione Transport

[Devlin-Moyer]

Main improvements in this PR:

As proposed in #722:

• Removes MAR04940 and MAR06391
• Adds new gene entries for SLC25A39 (ENSG00000013306) and SLC25A40 (ENSG00000075303)
• Edits MAR08771 to be MAM02026c --> MAM02026m, GPR: ENSG00000013306 or ENSG00000075303, RHEA:74819
• Merges annotations for MAR04940 and MAR06391 in reactions.tsv into those for MAR08771

I hereby confirm that I have:

• Tested my code on my own computer for running the model
• Selected develop as a target branch
• Any removed reactions and metabolites have been moved to the corresponding deprecated identifier lists

[Devlin-Moyer]

The Ensembl website seems to have gone down (for me, at least) right after I got all the transcript and protein IDs for SLC25A39, so at the moment genes.tsv currently only has the Ensembl Gene ID and the one Ensembl Transcript ID that was on the HGNC page for SLC25A40; I can update it later, whenever I can actually connect to Ensembl
nevermind; got them off of GeneCards

[haowang-bioinfo]

@Devlin-Moyer nice - all changes look good and didn't break anything