requests: remove an unused allowlist entry - #6911

Looks like a result of #6892.

Kind of annoying that requests is going to randomly fail stubtest every so often due to unrelated changes we make to the urllib stubs.

Would there be a way to make sure stubtest always runs for requests every time a change is made to the urllib stubs, so we're alerted to unused allowlist entries when the PR is being prepared?

Currently the stubs to be tested in a PR are given by:

STUBS=$(git diff --name-only origin/${{ github.base_ref }} HEAD | egrep ^stubs/ | cut -d "/" -f 2 | sort -u | (while read stub; do [ -d stubs/$stub ] && echo $stub || true; done))

We should probably replace this with a script that takes in account dependencies to types-foo packages specified in METADATA.toml.