Revert "XFAIL clang-args-transitive-availability.swift"

This reverts commit 6a9e2d4.

Author: hamishknight

test/ModuleInterface/clang-args-transitive-availability.swift

@@ -10,8 +10,6 @@
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck %s < %t/deps.json
 
-// REQUIRES: rdar151740686
-
 import ImportsMacroSpecificClangModule
 
 // CHECK:      "directDependencies": [