feat(amneziawg): remove the vestigial routeThroughXray toggle from the UI

Hard cutover, part 4: the embedded path has no opt-in gate for Xray
routing at all (every peer's traffic already goes through Xray's own
SOCKS5 relay unconditionally -- see xray.go's injectAmneziawgnetSocks), so
a toggle that no longer does anything would just confuse admins. Removed
from the form (amneziawg.tsx), the per-protocol Zod schema and its
new-inbound default, and the routeThroughXray/routeThroughXrayHint i18n
strings across all 13 locales.

The Go-side field stays (see internal/amneziawg's ServerSettings/Instance,
already annotated as vestigial in the previous commit) for backward
compatibility with existing stored settings -- z.object's default
unknown-key stripping means the form simply drops it from an existing
inbound's settings on its next save, no migration needed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/web/translation/en-US.json

@@ -1771,8 +1771,6 @@
         "ipv6SubnetHint": "e.g. fd86:ea04:1115::/64. Required when IPv6 is enabled.",
         "ipv6ExternalInterface": "IPv6 External Interface",
         "ipv6ExternalInterfaceHint": "Host NIC for the NDP proxy entries. Leave empty to reuse External Interface.",
-        "routeThroughXray": "Route through Xray",
-        "routeThroughXrayHint": "Off by default: the tunnel has no dependency on Xray at all. When on, every client's traffic is redirected into this inbound's own Xray bridge, and the actual outbound is chosen from the Routing page like any other protocol.",
         "obfuscation": "Obfuscation parameters",
         "regenerateObfuscation": "Regenerate",
         "jc": "Jc (junk packet count)",