Revert "http: simplify drain()"

This reverts commit bdf07f43.

The commit causes somewhat rampant MaxListenerExceeded warnings on fairly generic npm installs.

Fixes: https://github.com/nodejs/node/issues/29239

Collaborators: 👍 here to fast-track

@mcollina @targos

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines