Revert of Adding the chrome://suggestions test page. (https://codereview.chromium.org/163953005/)

Reason for revert:
SuggestionsCombinerTest.TestSuite and SuggestionsCombinerTest.SourcesAreNotDoneFetching crashing on Linux clang, as well as some Mac bots.

Original issue's description:
> The test page requires proper Canary flag to be set. See SuggestionsService::IsEnabled().
> 
> Details:
> - Changing the interface of SuggestionsService, so results are returned via callbacks. Also updating tests.
> - To support calls to SuggestionsService::FetchSuggestionsData() while data fetch takes place, we queue callbacks, and serve all data when data fetch completes.
> - Adding SuggestionsService::Shutdown() to handle mid-flight shutdown.
> - Making chrome://suggestions unavailable for incognito mode.
> 
> BUG=None
> Test=SuggestionsServiceTest
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251935

TBR=mathp@chromium.org,beaudoin@chromium.org,jered@chromium.org,sky@chromium.org,huangs@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=None

Review URL: https://codereview.chromium.org/170743009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251950 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251950