refactor(inbounds): drop the single-user shadowsocks inbound paths

isSSMultiUser treated 2022-blake3-chacha20-poly1305 as a single-user
inbound, and the inbounds page grew a row QR modal, a separate link
panel in the info modal and a client-count skip for that case. The
method is no longer allowed on inbounds, so every shadowsocks inbound
carries clients and those paths cannot be reached: remove them along
with the inbound-level QrCodeModal they alone opened.

frontend/src/test/protocol-capabilities.test.ts

@@ -8,7 +8,6 @@ import {
   canEnableStream,
   canEnableVisionSeed,
   isSS2022,
-  isSSMultiUser,
 } from '@/lib/xray/protocol-capabilities';
 
 // Pure-function tests for the capability predicates. Each fixture × stream
@@ -67,7 +66,6 @@ describe('protocol capability predicates', () => {
           canEnableStream: canEnableStream(values),
           canEnableVisionSeed: canEnableVisionSeed(values),
           isSS2022: isSS2022(values),
-          isSSMultiUser: isSSMultiUser(values),
         };
         expect(result).toMatchSnapshot();
       });