`iSynCJ816` is not valid SBML due to no flux objective and reaction with no reactants or products

[jonrkarr]

This can be fixed by

1. Replace

   <fbc:listOfObjectives fbc:activeObjective="obj">
     <fbc:objective fbc:id="obj" fbc:type="maximize">
       <fbc:listOfFluxObjectives/>
     </fbc:objective>
   </fbc:listOfObjectives>

   with

   <fbc:listOfObjectives fbc:activeObjective="obj_auto">
     <fbc:objective fbc:id="obj_auto" fbc:type="maximize">
       <fbc:listOfFluxObjectives>
         <fbc:fluxObjective fbc:reaction="R_BIOMASS_Ec_SynAuto_1" fbc:coefficient="1"/>
       </fbc:listOfFluxObjectives>
     </fbc:objective>
     <fbc:objective fbc:id="obj_mixo" fbc:type="maximize">
       <fbc:listOfFluxObjectives>
         <fbc:fluxObjective fbc:reaction="R_BIOMASS_Ec_SynMixo_1" fbc:coefficient="1"/>
       </fbc:listOfFluxObjectives>
     </fbc:objective>
     <fbc:objective fbc:id="obj_hetero" fbc:type="maximize">
       <fbc:listOfFluxObjectives>
         <fbc:fluxObjective fbc:reaction="R_BIOMASS_Ec_SynHetero_1" fbc:coefficient="1"/>
       </fbc:listOfFluxObjectives>
     </fbc:objective>
   </fbc:listOfObjectives>

2. Remove reaction R_DNADRAIN

   <reaction id="R_DNADRAIN" fast="false" reversible="false" name="Dna sink transport reaction" metaid="R_DNADRAIN" sboTerm="SBO:0000176" fbc:upperFluxBound="cobra_default_ub" fbc:lowerFluxBound="cobra_0_bound">
     <sbml:annotation xmlns:sbml="http://www.sbml.org/sbml/level3/version1/core">
       <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
         <rdf:Description rdf:about="#R_DNADRAIN">
           <bqbiol:is xmlns:bqbiol="http://biomodels.net/biology-qualifiers/">
             <rdf:Bag>
               <rdf:li rdf:resource="http://identifiers.org/bigg.reaction/DNADRAIN"/>
             </rdf:Bag>
           </bqbiol:is>
         </rdf:Description>
       </rdf:RDF>
     </sbml:annotation>
   </reaction>