remove CaseQueryMixin
remove CaseQueryMixin

it is now unused

puttarajubr/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,puttarajubr/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,puttarajubr/commcare-hq,dimagi/commcare-hq