nginx: fix provides

nginx: fix provides

nginx modules must not provide nginx which causes them to not be able
to be installed alongside nginx due to the new apk provide fixes.

Remove PROVIDES from modules.

Remove nginx-ssl from PROVIDES as there is no non-ssl variant, i.e. all
version provide ssl.

Set nginx-ssl as the default variant.

Remove non-existent config value.

Signed-off-by: George Sapkin <george@sapk.in>