Remove stale 'lib64' entries in browser_tests.isolate and chrome.isolate on linux

'lib32' was removed in r240867 because it was not being generated on OSX
anymore. These directories were likely generated by NaCl and stopped being
generated at some moment in the past days.

R=szym@chromium.org
BUG=

Review URL: https://codereview.chromium.org/113773005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241063 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241063