Test certificates are shipped in npm package

**Environment Information**
- OS [e.g. Mac, Arch, Windows 10]: Mac
- Node Version [e.g. 8.2.1]:v18.12.0
- NPM Version [e.g. 5.4.2]: 8.19.2
- C++ Toolchain [e.g. Visual Studio, llvm, g++]:
- node-rdkafka version [e.g. 2.3.3]: v2.16.1

**Steps to Reproduce**

The following certificates from the librdkafka dependency are flagged as sensitive data during the security scan:

https://github.com/confluentinc/librdkafka/blob/master/tests/fixtures/ssl/client2.certificate.pem
https://github.com/confluentinc/librdkafka/blob/master/tests/fixtures/ssl/client2.key

Were they included intentionally?

**node-rdkafka Configuration Settings**

**Additional context**

Start by inspecting the published npm package contents and the packaging or build configuration that brings in librdkafka. Check whether tests/fixtures/ssl/client2.certificate.pem and tests/fixtures/ssl/client2.key are included, then verify that the package no longer ships them while the required build and test behavior remains intact.

Written by the indexing model from the issue text.