Remove casts of AVL function pointers.

libraries/libavl/testavl.c

libraries/librewrite/var.c

servers/slapd/at.c

servers/slapd/back-bdb/attr.c

servers/slapd/back-bdb/cache.c

servers/slapd/back-bdb/dn2id.c

servers/slapd/back-bdb/idl.c

servers/slapd/back-ldap/back-ldap.h

servers/slapd/back-ldap/init.c

servers/slapd/back-ldbm/attr.c

servers/slapd/back-ldbm/cache.c

servers/slapd/back-meta/init.c

servers/slapd/back-sql/entry-id.c

servers/slapd/back-sql/schema-map.c

servers/slapd/back-sql/search.c

servers/slapd/back-sql/sql-wrap.c

servers/slapd/cr.c

servers/slapd/entry.c

servers/slapd/mr.c

servers/slapd/oc.c