Remove readonly reaction.metabolites dict for now
Remove readonly reaction.metabolites dict for now

dictproxy had issues on macs, need a different solution

aebrahim/cobrapy,zakandrewking/cobrapy,JuBra/cobrapy,aebrahim/cobrapy,jeicher/cobrapy,JuBra/cobrapy,jerkos/cobrapy,jerkos/cobrapy,zakandrewking/cobrapy,jeicher/cobrapy