n-api: remove unused Test function

Currently when building the following warning is emitted:

../test_symbol.c:4:19:
warning: unused function 'Test' [-Wunused-function]
static napi_value Test(napi_env env, napi_callback_info info) {
                  ^
1 warning generated.

This commit removes this unused function.

PR-URL: https://github.com/nodejs/node/pull/20320


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>