Clean up the deprecation warning for Request.context

Request.context is already removed in M46 and thus the deprecation message
string is no longer needed.

BUG=515786

Review URL: https://codereview.chromium.org/1373713004

Cr-Commit-Position: refs/heads/master@{#361254}

third_party/WebKit/Source/core/frame/UseCounter.cpp

@@ -931,9 +931,6 @@ String UseCounter::deprecationMessage(Feature feature)
     case PrefixedPerformanceResourceTimingBufferFull:
         return replacedBy("Performance.onwebkitresourcetimingbufferfull", "Performance.onresourcetimingbufferfull");
 
-    case FetchAPIRequestContext:
-        return "Request.context is deprecated and will be removed in M46 (see: https://www.chromestatus.com/feature/5534702526005248).";
-
     case HeaderValueNotMatchingRFC7230:
         return "Header values not matching to RFC 7230, will be deprecated (see: https://www.chromestatus.com/feature/6457425448140800).";
 

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -779,7 +779,6 @@ public:
         CSSValuePrefixedMaxContent = 922,
         CSSValuePrefixedFitContent = 923,
         CSSValuePrefixedFillAvailable = 924,
-        FetchAPIRequestContext = 925,
         PresentationDefaultRequest = 926,
         PresentationAvailabilityChangeEventListener = 927,
         PresentationRequestConstructor = 928,