nginx: enable ssl for all variants and remove nginx-util w/o ssl

nginx: enable ssl for all variants and remove nginx-util w/o ssl

Make the plain nginx version the same as nginx-ssl.
In a further change we will replace nginx by a dummy package,
depending on +nginx-ssl instead. This allows a smooth upgrade.

For nginx-util leave the ssl and the ssl-nopcre versions only.
For nginx-mod-luci remove the duplicate ssl version.
Replace the removed packages by dummies for a smooth upgrade.
The dummy packages will be removed after a transition period.

Additionally, enable the http2 module for nginx-ssl by default
and cleanup the nginx.init file.

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>