Remove some old support for PNaCl Scons browser tests.

ppapi/native_client/tools/browser_tester/browsertester/browserlauncher.py

 #!/usr/bin/python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os.path
 import re
 import shutil
 import sys
 import tempfile
@@ skipping 170 matching lines @@
       raise LaunchFailure('Browser does not exist %r'% browser_path)
     if not os.access(browser_path, os.X_OK):
       raise LaunchFailure('Browser cannot be executed %r (Is this binary on an '
                           'NFS volume?)' % browser_path)
     if self.options.sel_ldr:
       env['NACL_SEL_LDR'] = self.options.sel_ldr
     if self.options.sel_ldr_bootstrap:
       env['NACL_SEL_LDR_BOOTSTRAP'] = self.options.sel_ldr_bootstrap
     if self.options.irt_library:
       env['NACL_IRT_LIBRARY'] = self.options.irt_library
-    if self.options.prefer_portable_in_manifest:
-      env['NACL_PREFER_PORTABLE_IN_MANIFEST'] = '1'
     self.SetStandardStream(env, 'NACL_EXE_STDIN',
                            self.options.nacl_exe_stdin, False)
     self.SetStandardStream(env, 'NACL_EXE_STDOUT',
                            self.options.nacl_exe_stdout, True)
     self.SetStandardStream(env, 'NACL_EXE_STDERR',
                            self.options.nacl_exe_stderr, True)
     print 'ENV:', ' '.join(['='.join(pair) for pair in env.iteritems()])
     print 'LAUNCHING: %s' % ' '.join(cmd)
     sys.stdout.flush()
     self.browser_process = RunCommand(cmd, env=env)
@@ skipping 130 matching lines @@
              '--trace-children=yes',
              '--nacl-file=%s' % (self.options.files[0],),
              '--ignore=../tools/valgrind/tsan/ignores.txt',
              '--suppressions=../tools/valgrind/tsan/suppressions.txt',
              '--log-file=%s/log.%%p' % (self.tool_log_dir,)] + cmd
     elif self.options.tool != None:
       raise LaunchFailure('Invalid tool name "%s"' % (self.options.tool,))
     cmd.extend(self.options.browser_flags)
     cmd.append(url)
     return cmd