Fix sign in validation error copy (#831)

These errors were injecting devise's authentication_keys which includes email and was duplicating that copy, for example:

"Incorrect email email or password"

config/locales/devise.en.yml

@@ -9,10 +9,10 @@ en:
     failure:
       already_authenticated: "You are already signed in"
       inactive: "Your account has not been activated yet"
-      invalid: "Incorrect %{authentication_keys} email or password"
+      invalid: "Incorrect %{authentication_keys} or password"
       locked: "Your account has been locked."
       last_attempt: "You have one more attempt before your account is locked"
-      not_found_in_database: "Incorrect %{authentication_keys} email or password"
+      not_found_in_database: "Incorrect %{authentication_keys} or password"
       timeout: "Your session expired. Sign in again to continue."
       unauthenticated: "You need to sign in or sign up before continuing"
       unconfirmed: "You must confirm your email address before continuing"