Remove EOL'd nginx 1.16.x and 1.17.x
Remove EOL'd nginx 1.16.x and 1.17.x

Resolves #351
Resolves #366

Signed-off-by: Arjun Sreedharan <29ce4cd6ea5d13cdc653e7ecc5dd8b599d496b8a@vmware.com>

cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack