Remove all non-prod files from distribution

[jeffalder]

When installing ssh2, the tests and test fixtures are all installed. This doesn't feel desirable, as it puts test keys, example code, and other data into the runtime environment.

This change will pack only the lib directory, but that does include LICENSE, package.json, and README.md per npm. See https://docs.npmjs.com/cli/v10/using-npm/developers#keeping-files-out-of-your-package for more information.

Running npm pack gave me a tarball with these files:

package/LICENSE
package/lib/protocol/crypto/src/binding.cc
package/lib/protocol/crypto/binding.gyp
package/lib/agent.js
package/lib/Channel.js
package/lib/client.js
package/lib/protocol/constants.js
package/lib/protocol/crypto.js
package/lib/protocol/handlers.js
package/lib/protocol/handlers.misc.js
package/lib/http-agents.js
package/lib/index.js
package/lib/protocol/kex.js
package/lib/keygen.js
package/lib/protocol/keyParser.js
package/lib/protocol/node-fs-compat.js
package/lib/protocol/crypto/poly1305.js
package/lib/protocol/Protocol.js
package/lib/server.js
package/lib/protocol/SFTP.js
package/lib/protocol/utils.js
package/lib/utils.js
package/lib/protocol/zlib.js
package/package.json
package/README.md

Let me know if anything is missing.

[mscdex]

Duplicate of #1217