http: replace superfluous property with getter/setter

[ronag]

Slightly reduces memory overhead by replacing superfluous property with getter/setter.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[mscdex]

AFAIK getters/setters like this incur noticeable overhead, so perhaps we should be adjusting the documentation to more strongly recommend socket over connection.

[mscdex]

Also if we're making this change we should also replace all usage of .connection in core with .socket to avoid the overhead.

[ronag]

@mscdex better?

[ronag]

@Trott: this seems ready

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/25046/

[Trott]

Landed in 0daec61