purT curation notes

• UniProt identifies Q88MW1 as Formate-dependent phosphoribosylglycinamide formyltransferase [file:PSEPK/purT/purT-uniprot.txt "RecName: Full=Formate-dependent phosphoribosylglycinamide formyltransferase"].
• PurT uses formate, ATP, and GAR rather than the folate-bound donor used by PurN
  PMID:8117714.
• Remove GO:0004644 and GO:0016742: they place the EC 6.3.1.21 C-N ligase in
  folate-dependent transferase chemistry. Replace the generic catalytic/process terms
  with GO:0043815 and GO:0006189; retain nucleotide, ATP, magnesium, and metal
  binding as non-core.
• Open question: Under which carbon and folate conditions does PurT rather than PurN provide most GAR transformylase flux?