Merge `HIDDEN_SERVICE_VIA_TRANSPARENT_PROXY` into `ALLOW_ACCESS_TO_HIDDEN_SERVICE` (#7901)

If Mastodon accesses to the hidden service via transparent proxy, it's needed to avoid checking whether it's a private address, since `.onion` is resolved to a private address.
I was previously using the `HIDDEN_SERVICE_VIA_TRANSPARENT_PROXY` to provide that function. However, I realized that using `HIDDEN_SERVICE_VIA_TRANSPARENT_PROXY` is redundant, since this specification is always used with `ALLOW_ACCESS_TO_HIDDEN_SERVICE`. Therefore, I decided to integrate the setting of `HIDDEN_SERVICE_VIA_TRANSPARENT_PROXY` into` ALLOW_ACCESS_TO_HIDDEN_SERVICE`.