Remove HTTP keepAliveTimeout workaround not needed since Node.js 12 (#52561)

Summary:

The removed code comment is pretty clear that this workaround is in place for a specific bug, which was closed in a Node.js 8.x minor: https://github.com/nodejs/node/issues/13391

A related issue descibed a problem that still existed in Node 10:
https://github.com/nodejs/node/issues/27363

Subsequent comments reporting problems with newer Node.js versions all seem to relate to mismatched configuration with load balancers, not directly relevant to Metro.

Reproducers for the original bugs no longer repro on new Node.js (tested with 22.14), so I think it's safe to conclude this is fixed.

Changelog: [Internal]

Differential Revision: D78158427