cleanup struct declarations

servers/slapd/abandon.c

servers/slapd/at.c

servers/slapd/back-meta/back-meta.h

servers/slapd/back-monitor/back-monitor.h

servers/slapd/back-monitor/compare.c

servers/slapd/back-relay/op.c

servers/slapd/back-shell/shell.h

servers/slapd/backend.c

servers/slapd/cancel.c

servers/slapd/connection.c

servers/slapd/cr.c

servers/slapd/mr.c

servers/slapd/oc.c

servers/slapd/oidm.c

servers/slapd/operation.c

servers/slapd/overlays/syncprov.c

servers/slapd/proto-slap.h

servers/slapd/schema_prep.c

servers/slapd/sets.h

servers/slapd/slap.h