Fix simplified Linux tv-casting-app gn build error. (project-chip#34692)

Author: shaoltan-amazon

examples/tv-casting-app/linux/BUILD.gn

@@ -58,10 +58,12 @@ executable("chip-tv-casting-app") {
 
   if (chip_build_libshell) {
     defines += [ "ENABLE_CHIP_SHELL" ]
-    sources += [
-      "CastingShellCommands.cpp",
-      "CastingShellCommands.h",
-    ]
+    if (!chip_casting_simplified) {
+      sources += [
+        "CastingShellCommands.cpp",
+        "CastingShellCommands.h",
+      ]
+    }
   }
 
   output_dir = root_out_dir