Brave-browser: remove Google's sign-in workaround

[rebron]

Test plan

See https://github.com/brave/brave-core/pull/629

Description

Google added a new pref for sign-in with Chromium: 70.0.3538.45

Remove/hide from UI, default off to account for issues.

[petemill]

@rebron I don't think we want to remove the Prediction service settings. That was added back in to enable users to have autocomplete for search terms in the Location Bar. If we remove that (opt-in for Brave) then we won't be offering an autocomplete search term feature.

That at least would give us feature parity with muon.

"Allow Brave sign-in" - since that doesn't do anything then we should for sure remove it (and default to off in case of side-effects)

"Use a prediction service to load pages more quickly"
"Allow sites to check if you have payment methods saved"

• We don't provide these features in muon, but are we sure we don't want to offer them to our users?

[bbondy]

Agree with @petemill on everything, I think we just want to remove the allow Brave sign-in

[bsclifton]

++ on only removing Allow <> sign-in

[rebron]

Thanks @petemill I'll update the title and description to just remove Google sign-in and will get those items updated in the mock/spec

[LaurenWags]

Verified passed with

Brave | 0.55.14 Chromium: 70.0.3538.54 (Official Build) beta(64-bit)
-- | --
Revision | 4f8e578b6680574714e9ed3bb9f02922b4dde40d-refs/branch-heads/3538@{#937}
OS | Mac OS X

Verified with test plan from https://github.com/brave/brave-core/pull/629

Verification Passed on

Brave | 0.55.14 Chromium: 70.0.3538.54 (Official Build) beta(64-bit)
-- | --
Revision | 4f8e578b6680574714e9ed3bb9f02922b4dde40d-refs/branch-heads/3538@{#937}
OS | Linux

Verification passed on

Brave | 0.55.14 Chromium: 70.0.3538.54 (Official Build) beta(64-bit)
-- | --
Revision | 4f8e578b6680574714e9ed3bb9f02922b4dde40d-refs/branch-heads/3538@{#937}
OS | Windows 7