Remove ssl_generation_key for 2.x cleanup

Author: drbrain

lib/net/http/persistent.rb

@@ -427,11 +427,6 @@ def self.detect_idle_timeout uri, max = 10
 
   attr_reader :ssl_generation # :nodoc:
 
-  ##
-  # Where this instance's SSL connections live in the thread local variables
-
-  attr_reader :ssl_generation_key # :nodoc:
-
   ##
   # SSL session lifetime
 
@@ -523,9 +518,6 @@ def initialize name: nil, proxy: nil, pool_size: DEFAULT_POOL_SIZE
     @socket_options << [Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1] if
       Socket.const_defined? :TCP_NODELAY
 
-    key = ['net_http_persistent', name].compact
-    @ssl_generation_key = [key, 'ssl_generations'].join('_').intern
-
     @pool = Net::HTTP::Persistent::Pool.new size: pool_size do |http_args|
       Net::HTTP::Persistent::Connection.new Net::HTTP, http_args, @ssl_generation
     end