clean up serviceAccountName functions

These don't appear to be used anywhere:

$ grep -ir serviceAccountName  .
./qdb/templates/_helpers.tpl:{{- define "qdb.serviceAccountName" -}}
./mgm/templates/_helpers.tpl:{{- define "mgm.serviceAccountName" -}}
./fst/templates/_helpers.tpl:{{- define "fst.serviceAccountName" -}}
./fusex/templates/_helpers.tpl:{{- define "fusex.serviceAccountName" -}}
./sps/templates/_helpers.tpl:{{- define "sps.serviceAccountName" -}}