ADFA-4552: remove dead VpnService scaffolding (keep the live proxy)

[luisguzman-adfa]

Two different things called "VPN"

The old VpnService tunnel (TProxyService) no longer exists. Auditing every vpn reference showed the naming now covers two things:

• Dead / vestigial — never-reached VpnService permission plumbing + a log-only stub.
• Live — the prefs.getEnable() toggle (Control button) that applies a real WebView SOCKS proxy in PortalActivity (WebViewProxyConfigurator.applySocks) and proxied box pings.

This PR removes only the dead parts. The live proxy and its "VPN"-flavoured names (btn_vpn_* colors, vpn_starting/vpn_stopping/vpn_description, control_enable/disable, isVpnActive, prepareVpn() whose body is a live battery prompt) are intentionally left as-is; renaming belongs with the rebrand strings audit.

Removed (dead)

• MainActivity: unused import android.net.VpnService; the vpnPermissionLauncher field + its registerForActivityResult(...) block (registered but never .launch()ed); and connectVpn() (logs vpn_permission_granted, reachable only from that launcher). Its BatteryUtils.checkAndPromptOptimizations call is already covered by batteryOptLauncher + prepareVpn(), so nothing is lost.
• ServiceReceiver: the commented-out VpnService/TProxyService boot auto-start + now-unused VpnService/Build imports. Kept as a placeholder seam for ADFA-3340 (boot auto-start) with a TODO; header → AppDevForAll.
• strings.xml (values, es, fr, hi, pt, ru-rRU): vpn_permission_granted removed from all six locales together (no MissingTranslation risk).

Not touched (live)

prefs.getEnable()/setEnable(), the SOCKS proxy path, checkServerStatus proxy pings, UsageFragment Control button, btn_vpn_* colors, the three live vpn_* strings, prepareVpn().

Verification (sandbox)

• No remaining ref to connectVpn / vpnPermissionLauncher / vpn_permission_granted in controller/app/src.
• VpnService gone from code (only in ServiceReceiver comments as history).
• MainActivity brace balance 383/383; ServiceReceiver imports all used.
• No javac in sandbox (JRE only) — please build :app:lintDebug.

Notes

• ServiceReceiver is not currently registered in the manifest, so it doesn't fire today; ADFA-3340 will add the <receiver> + RECEIVE_BOOT_COMPLETED when wiring auto-start. Left as the intended hook point.
• lint-baseline.xml still has stale vpn entries; they simply stop matching after removal (baseline is a filter, not a gate).

Test (device)

1. Build + lint pass.
2. Control button still toggles the tunnel/proxy on/off (label + red/green), portal routes through the SOCKS proxy when enabled, box pings work — unchanged.
3. First-run permission prompts → battery-optimization prompt still appears (via prepareVpn()/batteryOptLauncher).

Epic ADFA-1028. Author: AppDevForAll.