http: remove redundant condition

`conn.destroyed` is guaranteed to be `false` because a previous `if`
statement already handles the case where `conn && conn.destroyed`
evaluates to `true` returning `false` in that case.

PR-URL: https://github.com/nodejs/node/pull/29078


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>