rgw: move all reshard config options out of legacy_config_options

rgw: move all reshard config options out of legacy_config_options

With commit b713bb77a1d some rgw reshard config options were updated,
but corresponding changes were not made to
legacy_config_options. Since accesses to these config options were
mixed (both modern and legacy) it led to some inconsistencies. So we
remove the legacy options and made sure all accesses uses the modern
convention/coding.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>