fuzz: http_request workaround for libevent < 2.1.1

Summary:

Before libevent 2.1.1, internal functions names didn't end with an
underscore.

Backport of core PR18682.

Depends on D9000.

Test Plan:

ninja bitcoin-fuzzers

I can't test the fix since I have no system with an old enough libevent
that match our minimum requirements.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9001