Revert "stage2: Add apt-transport-https" (#304)

This reverts commit 1806504.

In Buster, APT has built‐in support for HTTPS repos (since version 1.5).
The ca-certificates package is already included in the modified file, so
this commit shouldn’t break anything.

stage2/01-sys-tweaks/00-packages

@@ -14,7 +14,6 @@ raspberrypi-sys-mods
 pi-bluetooth
 apt-listchanges
 usb-modeswitch
-apt-transport-https
 libpam-chksshpwd
 rpi-update
 libmtp-runtime