server: remove all internal mentions about "webui" (#24817)

tools/server/server-context.h

@@ -22,8 +22,7 @@ struct server_context_meta {
     bool has_inp_image;
     bool has_inp_audio;
     bool has_inp_video;
-    json json_ui_settings;            // Primary: new name
-    json json_webui_settings;            // Deprecated: use json_ui_settings instead (kept for backward compat)
+    json json_ui_settings;
     int slot_n_ctx;
     enum llama_pooling_type pooling_type;