Removed all references to "Google Wi-Fi Assistant" from Settings.

+ Removed Wi-Fi Assistant message in Wi-Fi Advanced since it was
overridden by the Wi-Fi Assistant.
+ Removed Wi-Fi Assistant message in Wi-Fi Assistant Card.  Instead,
it is programatically created when the scorer is known.
+ "Google" was replaced with a placeholder.

Bug: 17457236
Change-Id: If3aab06c911ecf6ec13cbf00dea2fe9333abc1fc