Incorrect handling of disallowConform in cluster specifications.

[bzbarsky-apple]

Steps to reproduce:

1. Add the following to src/app/zap-templates/zcl/data-model/chip/rvc-run-mode-cluster.xml in Matter:

   <features>
     <!-- TODO: ZAP still generates feature bits for things with disallowConform! -->
     <feature bit="0" code="DEPONOFF" name="OnOff" summary="Dependency with the OnOff cluster is disallowed for this cluster">
       <disallowConform/>
     </feature>
     <feature bit="16" code="DIRECTMODECH" name="DirectModeChange" summary="Cluster supports changing run modes from non-Idle states">
       <optionalConform/>
     </feature>
   </features>
   

2. Remove the Feature bitmap from that cluster.
3. Rerun codegen.

This generates a feature bit for the OnOff feature, even though it's explicitly listed as not allowed for this cluster.