feat: remove strip_received_headers config option

This previously removed all Received headers which were sent to the smtp
server when enabled. This is not something that should be happening.

lib/postal/smtp_server/client.rb

@@ -393,15 +393,10 @@ module Postal
                 if @header_key && @headers[@header_key.downcase] && @headers[@header_key.downcase].last
                   @headers[@header_key.downcase].last << data.to_s
                 end
-                # If received headers are configured to be stripped and we're currently receiving one
-                # skip the append methods at the bottom of this loop.
-                next if Postal.config.smtp_server.strip_received_headers? && @header_key && @header_key.downcase == "received"
               else
                 @header_key, value = data.split(/:\s*/, 2)
                 @headers[@header_key.downcase] ||= []
                 @headers[@header_key.downcase] << value
-                # As above
-                next if Postal.config.smtp_server.strip_received_headers? && @header_key && @header_key.downcase == "received"
               end
             end
             @data << data