fix(react-native-xcode): Use CONFIG_CMD if set (#46112)

Summary:
In the recent 0.75 release I've noticed new `CONFIG_CMD` option in `react-native-xcode.sh`. But this option was not used. Insted when set `CONFIG_APP` was used.

This seems like a bug. As the usage before this PR would be as follow:

```bash
export CONFIG_CMD=true
export CONFIG_APP="/path/to/node /path/to/node_modules/react-native/cli.js config"
```

After this PR

```
export CONFIG_CMD="/path/to/node /path/to/node_modules/react-native/cli.js config"
```

This PR also removed unused explicite `--config-cmd "$CONFIG"` flag, as this is always overwriten by the code above, by default to `--config-cmd" "$NODE_BINARY $NODE_ARGS $REACT_NATIVE_DIR/cli.js config`.

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[iOS][Fixed] - Use CONFIG_CMD if set

Pull Request resolved: https://github.com/facebook/react-native/pull/46112

Test Plan: I've set `CONFIG_CMD` and run Xcode Release build to check that the set command is executed.

Reviewed By: christophpurrer

Differential Revision: D61545010

Pulled By: blakef

fbshipit-source-id: ebbf8ebc08404bc6816277518a3b86c6f7e41e6e

packages/react-native/scripts/react-native-xcode.sh

@@ -141,7 +141,7 @@ fi
 if [[ -n "$CONFIG_JSON" ]]; then
   EXTRA_ARGS+=("--load-config" "$CONFIG_JSON")
 elif [[ -n "$CONFIG_CMD" ]]; then
-  EXTRA_ARGS+=("--config-cmd" "$CONFIG_APP")
+  EXTRA_ARGS+=("--config-cmd" "$CONFIG_CMD")
 else
   EXTRA_ARGS+=("--config-cmd" "$NODE_BINARY $NODE_ARGS $REACT_NATIVE_DIR/cli.js config")
 fi
@@ -149,7 +149,6 @@ fi
 # shellcheck disable=SC2086
 "$NODE_BINARY" $NODE_ARGS "$CLI_PATH" $BUNDLE_COMMAND \
   $CONFIG_ARG \
-  --config-cmd "$CONFIG" \
   --entry-file "$ENTRY_FILE" \
   --platform "$BUNDLE_PLATFORM" \
   --dev $DEV \