remove apt-transport-https from pre_reqs

[thaJeztah]

• relates to engine/install: remove apt-transport-https from instructions docs#13718
• fixes Is apt-transport-https a requirement on raspbian? #224

This package is no longer needed on all current distro versions we support. From the package description (https://packages.debian.org/buster/apt-transport-https);

This is a dummy transitional package - https support has been moved into the
apt package in 1.5. It can be safely removed.

Verifying the version of apt that's available in Ubuntu and Debian:

Ubuntu:

docker run --rm ubuntu:xenial apt --version
apt 1.2.35 (amd64)

docker run --rm ubuntu:17.04 apt --version
apt 1.4.6 (amd64)

docker run --rm ubuntu:17.10 apt --version
apt 1.5.2 (amd64)

docker run --rm ubuntu:18.04 apt --version
apt 1.6.14 (amd64)

docker run --rm ubuntu:20.04 apt --version
apt 2.0.6 (amd64)

Debian:

docker run --rm debian:stretch apt --version
apt 1.4.11 (amd64)

docker run --rm debian:buster apt --version
apt 1.8.2.3 (amd64)

docker run --rm debian:bullseye apt --version
apt 2.2.4 (amd64)

From the above; all currently supported versions of Ubuntu (18.04 and up), and Debian (old-stable and stable) have apt > 1.5, so we can remove this dependency from the installation instructions.