Remove invalid characters from ECDA JWK test.
Remove invalid characters from ECDA JWK test.

JWK uses the "base64url" encoding, so unlike 'base64' encoding the characters '/' and '+' are not allowed.

BUG=378034
TBR=rsleevi@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/755773002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@185906 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs