[Nginx] Should not define a default charset

[EtienneM]

We define a charset in the default Nginx configuration (https://github.com/Scalingo/php-buildpack/blob/master/conf/nginx/base.conf.erb#L83).

But then, If a user adds that kind of call in its code:

header("content-type:text/html; charset=iso-8859-1" );

The HTTP response will contain the header:

Content-Type: text/html; charset=UTF-8

Is it possible to remove this line?

https://app.intercom.io/a/apps/w4oogu7s/inbox/inbox/all/conversations/24705196813