[webcrypto] Simplify the AES-KW workaround for NSS and remove valgrind suppression

BUG=349939,245025

Review URL: https://codereview.chromium.org/210463003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@259153 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed