Cut FOR_EACH_KV

Summary: [Folly] Cut the FOR_EACH_KV macro, which may be replaced by a combination of range-for and structured bindings.

Differential Revision: D21826182

fbshipit-source-id: ce4712afd3d0d7806eb1fca8c97009da117f982e

.clang-format

@@ -42,7 +42,7 @@ ContinuationIndentWidth: 4
 Cpp11BracedListStyle: true
 DerivePointerAlignment: false
 DisableFormat:   false
-ForEachMacros:   [ FOR_EACH, FOR_EACH_KV, FOR_EACH_R, FOR_EACH_RANGE, ]
+ForEachMacros:   [ FOR_EACH, FOR_EACH_R, FOR_EACH_RANGE, ]
 IncludeCategories:
   - Regex:           '^<.*\.h(pp)?>'
     Priority:        1