Remove session_alloc (API Change)

* session_alloc is removed, as it does not improve
  performance as intended.

Actions Required:

* Don't use session_alloc

test/example/common/CMakeLists.txt

@@ -20,7 +20,6 @@ add_executable (tests-example-common
     Jamfile
     root_certificates.cpp
     server_certificate.cpp
-    session_alloc.cpp
 )
 
 set_property(TARGET tests-example-common PROPERTY FOLDER "tests")

test/example/common/Jamfile

@@ -10,7 +10,6 @@
 local SOURCES =
     root_certificates.cpp
     server_certificate.cpp
-    session_alloc.cpp
     ;
 
 local RUN_TESTS ;

test/example/common/session_alloc.cpp

@@ -1,12 +0,0 @@
-//
-// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-// Official repository: https://github.com/boostorg/beast
-//
-
-// Test that header file is self-contained.
-#include "example/common/session_alloc.hpp"
-