test: Removed server.start in grpc tests as it is deprecated and no longer needed

[bizob2828]

Description

I noticed when adding support for Node 22 we had some deprecation warnings.

(node:98461) DeprecationWarning: Calling start() is no longer necessary. It can be safely omitted.
(Use `node --trace-deprecation ...` to show where the warning was created)

When adding --trace-deprecation to the entire integration run I discovered

(node:99014) DeprecationWarning: Calling start() is no longer necessary. It can be safely omitted.
    at /Users/revans/code/pull-requests/node-newrelic/test/integration/grpc/reconnect.tap.js:221:16
    at /Users/revans/code/pull-requests/node-newrelic/node_modules/@grpc/grpc-js/src/server.ts:869:11
    at processTicksAndRejections (node:internal/process/task_queues:95:5)

It also existed in another grpc test.

How to Test

node test/integration/grpc/reconnect.tap.js

The deprecation warning is gone.

Additional Information

There is still this warning

(node:20389) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)

But it is safe because if/when Node.js removes punycode the unicode-length package will use its 3rd party dep of punycode based on this copy

⚠️ Note that userland modules don't hide core modules. For example, require('punycode') still imports the deprecated core module even if you executed npm install punycode. Use require('punycode/') to import userland modules rather than core modules.

[jsumners-nr]

Looks good to me.